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Which conductors connects the consumer’s terminals to distribution?
A. service mains
B. distributors
C. feeders
D. none of the above
The underground system cannot be operated above which voltage level?
A. 440 V
B. 66 KV
C. 33 KV
D. 11 KV
Overhead lines can be designed for operation upto:
A. 11 KV
B. 400 KV
C. 66 KV
D. 33 KV
F(s) = s2 – 1 / -s + 8 :what type of function ?
A. It is a PR function
B. it is not a PR function
C. data insufficient
D. none of these
Frequency of the given waveform is?
[pic]
A. 10 Hz
B. 100 Hz
C. 5 Hz
D. 0.1 Hz
Correct Answer: Option A, since it is a periodic but non alternating waveform hence here the time period is T = 100 msec. f = 1/T = 1/ 100 X 10-3 = 10Hz.
A 100 ohm resistor is directly connected across a 80 V battery. What is the power dissipitation?
A. 64 W
B. 1 W
C. 10 W
D. 5 W
Option A, I = V / R = 80 / 100 = 0.8 A ; so power = I2 R = 64 W.
1. The use of _____ instruments is merely confined within laboratories as standardizing instruments.
(a) Absolute
(b) indicating
(c) recording
(d) integrating
(e) none of the above
Ans: a
2. Which of the following instruments indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured?
(a) Absolute instruments
(b) Indicating instruments
(c) Recording instruments
(d) Integrating instruments
Ans: b
3. _____ Instruments are those which measure the total quantity of electricity delivered in a particular time.
(a) Absolute
(b) Indicating
(c) Recording
(d) Integrating
Ans: d
4. Which of the following are integrating instruments?
(a) Ammeters
(b) Voltmeters
(c) Wattmeters
(d) Ampere-hour and watt-hour meters
Ans: d
5. Resistances can be measured with the help of
(a) wattmeters
(b) voltmeters
(c) ammeters
(d) ohmmeters and resistance bridges
(e) all of the above
Ans: d
6 According to application, instruments are classified as
(a) switch board
(b) portable
(c) both (a) and (b)
(d) moving coil
(e) moving iron
(f) both (d) and (e)
Ans: c
7. Which of the following essential features is possessed by an indicating instrument?
(a) Deflecting device
(b) Controlling device
(c) Damping device
(d) All of the above
Ans: d
8. A _____ device prevents the oscillation of the moving system and enables the latter to reach its final position quickly
(a) deflecting
(b) controlling
(c) damping
(d) any of the above
Ans: c
9. The spring material used in a spring control device should have the following property.
(a) Should be non-magnetic
(b) Most be of low temperature co-efficient
(c) Should have low specific resistance
(d) should not be subjected to fatigue
(e) All of the above
Ans: e
10. Which of the following properties damping oil must possess?
(a) Must be a good insulator
(b) Should be non-evaporating
(c) Should not have corrosive action upon the metal of the vane
(d) The viscosity of the oil should not change with the temperature
(e) All of the above
Ans: e
11. A moving-coil permanent-magnet instrument can be used as _____ by using a low resistance shunt.
(a) Ammeter
(b) voltmeter
(c) flux-meter
(d) ballistic galvanometer
Ans: a
12. A moving-coil permanent-magnet instrument can be used as flux-meter
(a) by using a low resistance shunt
(b) by using a high series resistance
(c) by eliminating the control springs
(d) by making control springs of large moment of inertia
Ans: c
13. Which of the following devices may be used for extending the range of instruments?
(a) Shunts
(b) Multipliers
(c) Current transformers
(d) Potential transformers
(e) All of the above
Ans: e
14. An induction meter can handle current upto
(a) 10 A
(b) 30 A
(c) 60 A
(d) 100 A
Ans: d
15. For handling greater currents induction wattmeters are used in conjunction with
(a) potential transformers
(b) current transformers
(c) power transformers
(d) either of the above
(e) none of the above
Ans: b
16. Induction type single phase energy meters measure electric energy in
(a) KW
(b) Wh
(c) kWh
(d) VAR
(e) None of the above
Ans: c
17. Most common form of A.C. meters met with in every day domestic and industrial installations are
(a) mercury motor meters
(b) Commutator motor meters
(c) induction type single phase energy meters
(d) all of the above
Ans: c
18. Which of the following meters are not used on D.C. circuits
(a) Mercury motor meters
(b) Commutator motor meters
(c) Induction meters
(d) None of the above
Ans: c
19. Which of the following is an essential part of a motor meter?
(a) An operating torque system
(b) A braking device
(c) Revolution registering device
(d) All of the above
Ans: d
20. A potentiometer may be used for
(a) measurement of resistance
(b) measurement of current
(c) calibration of ammeter
(d) calibration of voltmeter
(e) all of the above
Ans: e
21 is an instrument which measures the insulation resistance of an electric circuit relative to earth and one another,
(a) Tangent galvanometer
(b) Megger
(c) Current transformer
(d) None of the above
Ans: b
22. The household energy meter is
(a) an indicating instrument
(b) a recording instrument
(c) an integrating instrument
(d) none of the above
Ans: c
23. The pointer of an indicating instrument should be
(a) very light
(b) very heavy
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
24. The chemical effect of current is used in
(a) D.C. ammeter hour meter
(b) D.C. ammeter
(c) D.C. energy meter
(d) none of the above
Ans: a
25. In majority of instruments damping is provided by
(a) fluid friction
(b) spring
(c) eddy currents
(d) all of the above
Ans: c
26. An ammeter is a
(a) secondary instrument
(b) absolute instrument
(c) recording instrument
(d) integrating instrument
Ans: a
27. In a portable instrument, the controlling torque is provided by
(a) spring
(b) gravity
(c) eddy currents
(d) all of the above
Ans: a
28. The disc of an instrument using eddy current damping should be of
(a) conducting and magnetic material
(b) non-conducting and magnetic material
(c) conducting and non-magnetic material
(d) none of the above
Ans: c
29. The switch board instruments
(a) should be mounted in vertical position
(6) should be mounted in horizontal position
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
30. The function of shunt in an ammeter is to
(a) by pass the current
(b) increase the sensitivity of the ammeter
(c) increase the resistance of ammeter
(d) none of the above
Ans: a
31. The multiplier and the meter coil in a voltmeter are in
(a) series
(b) parallel
(c) series-parallel
(d) none of the above
Ans: a
32. A moving iron instrument can be used for
(a) D.C. only
(b) A.C. only
(c) both D.C. and A.C.
Ans: c
33. The scale of a rectifier instrument is
(a) linear
(b) non-linear
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
34. For measuring current at high frequency we should use
(a) moving iron instrument
(b) electrostatic instrument
(c) thermocouple instrument
(d) none of the above
Ans: c
35. The resistance in the circuit of the moving coil of a dynamometer wattmeter should be
(a) almost zero
(b) low
(c) high
(d) none of the above
Ans: c
36. A dynamometer wattmeter can be used for
(a) both D.C. and A.C.
(b) D.C. only
(c) A.C. only
(d) any of the above
Ans: a
37. An induction wattmeter can be used for
(a) both D.C. and A.C.
(6) D.C. only
(c) A.C. only
(d) any of the above
Ans: b
38. The pressure coil of a wattmeter should be connected on the supply side of the current coil when
(a) load impedance is high
(b) load impedance is low
(c) supply voltage is low
(d) none of the above
Ans: a
39. In a low power factor wattmeter the pressure coil is connected
(a) to the supply side of the current coil
(b) to the load side of the current coil
(c) in any of the two meters at connection
(d) none of the above
Ans: b
40. In a low power factor wattmeter the compensating coil is connected
(a) in series with current coil
(b) in parallel with current coil
(c) in series with pressure coil
(d) in parallel with pressure coil
Ans: c
41. In a 3-phase power measurement by two wattmeter method, both the watt meters had identical readings. The power factor of the load was
(a) unity
(6) 0.8 lagging
(c) 0.8 leading
(d) zero
Ans: a
42. In a 3-phase power measurement by two wattmeter method the reading of one of the wattmeter was zero. The power factor of the load must be
(a) unity
(b) 0.5
(c) 0.3
(d) zero
Ans: b
43. The adjustment of position of shading bands, in an energy meter is done to provide
(a) friction compensation
(b) creep compensation
(c) braking torque
(d) none of the above
Ans: a
44. An ohmmeter is a
(a) moving iron instrument
(b) moving coil instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
45. When a capacitor was connected to the terminal of ohmmeter, the pointer indicated a low resistance initially and then slowly came to infinity position. This shows that capacitor is
(a) short-circuited
(b) all right
(c) faulty
Ans: b
46. For measuring a very high resistance we should use
(a) Kelvin's double bridge
(b) Wheat stone bridge
(c) Megger
(d) None of the above
Ans: c
47. The electrical power to a meggar is provided by
(a) battery
(b) permanent magnet D.C. generator
(c) AC. generator
(d) any of the above
Ans: b
48. In a meggar controlling torque is provided by
(a) spring
(b) gravity
(c) coil
(d) eddy current
Ans: c
49. The operating voltage of a meggar is about
(a) 6 V
(b) 12 V
(c) 40 V
(d) 100 V
Ans: d
50. Murray loop test can be used for location of
(a) ground fault on a cable
(b) short circuit fault on a cable
(c) both the ground fault and the short-circuit fault
(d) none of the above
Ans: c
51. Which of the following devices should be used for accurate measurement of low D.C. voltage?
(a) Small range moving coil voltmeter
(b) D.C. potentiometer
(c) Small range thermocouple voltmeter
(d) None of the above
Ans: b
52. It is required to measure the true open circuit e.m.f. of a battery. The best device is
(a) D.C. voltmeter
(b) Ammeter and a known resistance
(c) D.C. potentiometer
(d) None of the above
Ans: c
53. A voltage of about 200 V can be measured
(a) directly by a D.C. potentiometer
(b) a D.C. potentiometer in conjunction with a volt ratio box
(c) a D.C. potentiometer in conjunction with a known resistance
(d) none of the above
Ans: b
54. A direct current can be measured by
(a) a D.C. potentiometer directly
(b) a D.C. potentiometer in conjunction with a standard resistance
(c) a D.C. potentiometer in conjunction with a volt ratio box
(d) none of the above
Ans: b
55. To measure a resistance with the help of a potentiometer it is
(a) necessary to standardise the potentiometer
(b) not necessary to standardise the potentiometer
(c) necessary to use a volt ratio box in conjunction with the potentiometer
(d) none of the above
Ans: b
56. A phase shifting transformer is used in conjunction with
(a) D.C. potentiometer
(b) Drysdale potentiometer
(c) A.C. co-ordinate potentiometer
(d) Crompton potentiometer
Ans: b
57. Basically a potentiometer is a device for
(a) comparing two voltages
(b) measuring a current
(c) comparing two currents
(d) measuring a voltage
(e) none of the above
Ans: a
58. In order to achieve high accuracy, the slide wire of a potentiometer should be
(a) as long as possible
(b) as short as possible
(c) neither too small not too large
(d) very thick
Ans: a
59. To measure an A. C. voltage by using an A.C. potentiometer, it is desirable that the supply for the potentiometer in taken
(a) from a source which is not the same as the unknown voltage
(b) from a battery
(c) from the same source as the unknown voltage
(d) any of the above
Ans: c
60. The stator of phase shifting transformer for use in conjunction with an A.C. potentiometer usually has a
(a) single-phase winding
(b) two-phase winding
(c) three-phase winding
(d) any of the above
Ans: b
61. In an AC. co-ordinate potentiometer, the currents in the phase and quadrature potentiometer are adjusted to be
(a) out of phase by 90°
(6) out of phase by 60°
(c) out of phase by 30°
(d) out of phase by 0°
(e) out of phase by 180°
Ans: a
62. A universal RLC bridge uses
(a) Maxwell bridge configuration for measurement of inductance and De Santas bridge for measurement of capacitance
(b) Maxwell Wein bridge for measurement of inductance and modified De Sauty's bridge for measurement of capacitance
(c) Maxwell Wein bridge for measurement of inductance and Wein bridge for measurement of capacitance
(d) Any of the above.
Ans: b
63. For measurements on high voltage capacitors, the suitable bridge is
(a) Wein bridge
(b) Modified De Sauty's bridge
(c) Schering bridge
(d) Any of the above
(e) None of the above
Ans: c
64. In an Anderson bridge, the unknown inductance is measured in terms of
(a) known inductance and resistance
(b) known capacitance and resistance
(c) known resistance
(d) known inductance
Ans: b
65. Wagner earthing device is used to eliminate errors due to
(a) electrostatic coupling
(b) electromagnetic coupling
(c) both (a) and (b)
(d) none of the above
Ans: a
66. For measurement of mutual inductance we can use
(a) Anderson bridge
(b) Maxwell's bridge
(c) Heaviside bridge
(d) Any of the above
Ans: c
67. For measurement of inductance having high value, we should use
(a) Maxwell's bridge
(b) Maxwell Wein bridge
(c) Hay's bridge
(d) Any of the above
Ans: c
68. If the current in a capacitor leads the voltage by 80°, the loss angle of the capacitor is
(a) 10°
(b) 80°
(c) 120°
(d) 170°
Ans: a
69. In a Schering bridge the potential of the detector above earth potential is
(a) a few volts only
(6) 1 kV
(c) 5 kV
(d) 10 kV
Ans: a
70. To avoid the effect of stray magnetic field in A.C. bridges we can use
(a) magnetic screening
(b) Wagner earthing device
(c) wave filters
(d) any of the above
Ans: a
71. If an inductance is connected in one arm of bridge and resistances in the remaining three arms
(a) the bridge can always be balanced
(b) the bridge cannot be balanced
(c) the bridge can be balanced if the resistances have some specific values
Ans: b
72. A power factor meter has
(a) one current circuit and two pressure circuits
(b) one current circuit and one pressure circuit
(c) two current circuits and one pressure circuit
(d) none of the above
Ans: a
73. The two pressure coils of a single phase power factor meter have
(a) the same dimensions and the same number of turns
(b) the same dimension but different number of turns
(c) the same number of turns but different dimensions
(d) none of the above
Ans: a
74. In a single phase power factor meter the phase difference between the currents in the two pressure coils is
(a) exactly 0°
(b) approximately 0°
(c) exactly 90°
(d) approximately 90°
Ans: c
75. In a dynamometer 3-phase power factor meter, the planes of the two moving coils are at
(a) 0°
(b) 60°
(c) 90°
(d) 120°
Ans: d
76. In a vibrating reed frequency meter the natural frequencies of two adjacent reeds have a difference of
(a) 0.1 Hz
(b) 0.25 Hz
(c) 0.5 Hz
(d) 1.5 Hz
Ans: c
77. In a Weston frequency meter, the magnetic axes of the two fixed coils are
(a) parallel
(b) perpendicular
(c) inclined at 60°
(d) inclined at 120°
Ans: b
78. A Weston frequency meter is
(a) moving coil instrument
(b) moving iron instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
79. A Weston synchronous scope is a
(a) moving coil instrument
(b) moving iron instrument
(c) dynamometer instrument
(d) none of the above
Ans: c
80. In a Weston synchronoscope, the fixed coils are connected across
(a) bus-bars
(b) incoming alternator
(c) a lamp
(d) none of the above
Ans: b
81. In Weston synchronoscope the moving coil is connected across
(a) bus-bars
(b) incoming alternator
(c) fixed coils
(d) any of the above
Ans: a
82. The power factor of a single phase load can be calculated if the instruments available are
(a) one voltmeter and one ammeter
(b) one voltmeter, one ammeter and one wattmeter
(c) one voltmeter, one ammeter and one energy meter
(d) any of the above
Ans: b
83. The desirable static characteristics of a measuring system are
(a) accuracy and reproducibility
(b) accuracy, sensitivity and reproducibility
(c) drift and dead zone
(d) static error
Ans: b
84. The ratio of maximum displacement deviation to full scale deviation of the instrument is called
(a) static sensitivity
(b) dynamic deviation
(c) linearity
(d) precision or accuracy
Ans: c
85. Systematic errors are
(a) instrumental errors
(b) environmental errors
(c) observational errors
(d) all of the above
Ans: d
86. Standard resistor is made from
(a) platinum
(b) maganin
(c) silver
(d) nichrome
Ans: b
87. Commonly used standard capacitor is
(a) spherical type
(b) concentric cylindrical type
(c) electrostatic type
(d) multilayer parallel plate type
Ans: b
88. Operating torques in analogue instruments are
(a) deflecting and control
(b) deflecting and damping
(c) deflecting, control and damping
(d) vibration and balancing
Ans: c
89. Commonly used instruments in power system measurement are
(a) induction
(b) moving coil or iron
(c) rectifier
(d) electrostatic Ans: a
90. Damping of the Ballistic galvanometer is made small to
(a) get first deflection large
(b) make the system oscillatory
(c) make the system critically damped
(d) get minimum overshoot
Ans: a
91. If an instrument has cramped scale for larger values, then it follows
(a) square law
(b) logarithmic law
(c) uniform law
(d) none of the above
Ans: b
92. Volt box is a component to
(a) extend voltage range
(6) measure voltage
(c) compare voltage in a box
(d) none of the above
Ans: a
93. E.m.f. of a Weston cell is accurately measured by
(a) electrostatic voltmeter
(b) hot wire voltmeter
(c) isothermal voltmeter
(d) electro dynamic voltmeter
Ans: a
94. The gravity controlled instrument has crowded scale because current is proportional to
(a) balancing weight
(b) deflection angle
(c) sine of deflection angle
Ans: c
95. A sensitive galvanometer produces large deflection for a
(a) small value of current
(b) large value of current
(c) large value of power
(d) large value of voltage
(e) none of the above
Ans: a
96. A multi range instrument has
(a) multiple shunt or series resistances inside the meter
(b) multi coil arrangement
(c) variable turns of coil
(d) multi range meters inside the measurement system
(e) any of the above
Ans: a
97. The rectifier instrument is not free from
(a) temperature error
(b) wave shape error
(c) frequency error
(d) all of the above
Ans: c
98. Alternating current is measured by
(a) induction ammeter
(b) permanent magnet type ammeter
(c) electrostatic ammeter
(d) moving iron repulsion type voltmeter
Ans: a
99. Most sensitive galvanometer is
(a) elastic galvanometer
(b) vibration galvanometer
(c) Duddlb galvanometer
(d) spot ballistic galvanometer
Ans: d
100. Instrument transformers are
(a) potential transformers
(b) current transformers
(c) both (a) and (b)
(d) power transformers
Ans: c
101. An instrument transformer is used to extend the range of
(a) induction instrument
(b) electrostatic instrument
(c) moving coil instrument
(d) any of the above
Ans: a
102. Wattmeter cannot be designed on the principle of
(a) electrostatic instrument
(b) thermocouple instrument
(c) moving iron instrument
(d) electro-dynamic instrument
Ans: c
103. In an energy meter braking torque is produced to
(a) safe guard it against creep
(b) brake the instrument
(c) bring energy meter to stand still
(d) maintain steady speed and equal to driving torque Ans: d
104. Various adjustments in an energy meter include
(a) light load or friction
(b) lag and creep
(c) overload and voltage compensation
(d) temperature compensation
(e) all of the above
Ans: e
105. The power of a n-phase circuit can be measured by using a minimum of
(a) (n - 1) wattmeter elements
(b) n wattmeter elements
(c) (n + 1) wattmeter elements
(d) 2n wattmeter elements
Ans: a
106. Two holes in the disc of energy meter are drilled at the opposite sides of the spindle to
(a) improve its ventilation
(b) eliminate creeping at no load
(c) increase its deflecting torque
(d) increase its braking torque
Ans: b
107. Which of the following is measured by using a vector voltmeter?
(a) Amplifier gain and phase shift
(b) Filler transfer functions
(c) Complex insersion loss
(d) All of the above
Ans: d
108. The principle on which vector voltmeter is based is
(a) that it works on the principle of complex variation
(b) that it measures the response of linear ramp voltage
(c) same as digital meter
(d) that it measures the amplitude of a single at two points and at the same time measures their phase difference
Ans: d
109. To measure radio frequency, the suitable frequency meter is
(a) Weston frequency meter
(b) reed vibrator frequency meter
(c) hetrodyne frequency meter
(d) electrical resonance frequency meter
Ans: c
Electromagnetic Induction
1. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as
(a) self-inductance
(b) mutual inductance
(c) series aiding inductance
(d) capacitance
Ans: a
2. As per Faraday's laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it
(a) lies perpendicular to the magnetic flux
(b) lies in a magnetic field
(e) cuts magnetic flux
(d) moves parallel to the direction of the magnetic field
Ans: c
3. Which of the following circuit element stores energy in the electromagnetic field ?
(a) Inductance
(b) Condenser
(c) Variable resistor
(d) Resistance
Ans: a
4. The inductance of a coil will increase under all the following conditions except
(a) when more length for the same number of turns is provided
(6) when the number of turns of the coil increase
(c) when more area for each turn is provided
(d) when permeability of the core increases
Ans: a
5. Higher the self-inductance of a coil,
(a) lesser its Weber-turns
(b) lower the e.m.f. induced
(c) greater the flux produced by it
(d) longer the delay in establishing steady current through it
Ans: d
6. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will
(a) increase
(b) decrease
(c) remain the same
(d) initially increase and then decrease
Ans: b
7. An open coil has
(a) zero resistance and inductance
(b) infinite resistance and zero inductance
(c) infinite resistance and normal inductance
(d) zero resistance and high inductance
Ans: b
8. Both the number of turns and the core length of an inductive coil are doubled.
Its self-inductance will be
(a) unaffected
(b) doubled
(c) halved
(d) quadrupled
Ans: b
9. If current in a conductor increases then according to Lenz's law self-induced voltage will
(a) aid the increasing current
(b) tend to decrease the amount of cur-rent
(c) produce current opposite to the in-creasing current
(d) aid the applied voltage
Ans: c
10. The direction of induced e.m.f. can be found by
(a) Laplace's law
(b) Lenz's law
(c) Fleming's right hand rule
(d) Kirchhoff s voltage law
Ans: b
11. Air-core coils are practically free from
(a) hysteresis losses
(b) eddy current losses
(c) both (a) and (b)
(d) none of the above
Ans: c
12. The magnitude of the induced e.m.f. in a conductor depends on the
(a) flux density of the magnetic field
(b) amount of flux cut
(c) amount of flux linkages
(d) rate of change of flux-linkages
Ans: d
13. Mutually inductance between two magnetically-coupled coils depends on
(a) permeability of the core
(b) the number of their turns
(c) cross-sectional area of their com-mon core
(d) all of the above
Ans: d
14. A laminated iron core has reduced eddy-current losses because
(a) more wire can be used with less D.C. resistance in coil
(b) the laminations are insulated from each other
(c) the magnetic flux is concentrated in the air gap of the core
(d) the laminations are stacked vertically
Ans: b
15. The law that the induced e.m.f. and current always oppose the cause producing them is due to
(a) Faraday
(b) Lenz
(c) Newton
(d) Coulomb
Ans: b
16. Which of the following is not a unit of inductance?
(a) Henry
(b) Coulomb/volt ampere
(c) Volt second per ampere
(d) All of the above
Ans: b
17. In case of an inductance, current is proportional to
(a) voltage across the inductance
(b) magnetic field
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: b
18. Which of the following circuit elements will oppose the change in circuit current ?
(a) Capacitance
(b) Inductance
(c) Resistance
(d) All of the above
Ans: b
19. For a purely inductive circuit which of the following is true ?
(a) Apparent power is zero
(b) Relative power is Zero
(c) Actual power of the circuit is zero
(d) Any capacitance even if present in the circuit will not be charged
Ans: c
20. Which of the following is unit of inductance?
(a) Ohm
(b) Henry
(c) Ampere turns
(d) Webers/metre
Ans: b
21. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be
(a) 64 A/s
(b) 32 A/s
(c) 16 A/s
(d) 4 A/s
Ans: d
22. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the inductance will be
(a) 3 mH
(b) 12 mH
(c) 24mH
(d)48mH
Ans: a
23. The self inductances of two coils are 8 mH and 18 mH. If the co-efficient of coupling is 0.5, the mutual inductance of the coils is
(a) 4 mH
(b) 5 mH
(c) 6 mH
(d) 12 mH
Ans: c
24. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be
(a) 32 mH
(b) 38 mH
(c) 40 mH
(d) 48 mH
Ans: b
25. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be
(a) 6 mH
(b) 14 mH
(c) 24 mH
(d) 48 mH
Ans: d
26. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Ans: c
27. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Ans: b
28. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Ans: d
29. A conductor 2 metres long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Ans: c
30. Lenz's law is a consequence of the law of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Ans: c
31. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Ans: b
32. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Ans: a
33. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils only
(c) mutual inductance and self inductance of two coils
(d) none of the above
Ans: c
34. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Ans: d
35. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Ans: c
36. Which of the following inductor will have the least eddy current losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Ans: a
37. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Ans: b
38. Two 300 uH coils in series without mutual coupling have a total inductance of
(a) 300 uH
(b) 600 uH
(c) 150 uH
(d) 75 uH
Ans: b
39. Current changing from 8 A to 12 A in one second induced 20 volts in a coil.
The value of inductance is
(a) 5 mH
(b) 10 mH
(c) 5 H
(d) 10 H
Ans: c
40. Which circuit element(s) will oppose the change in circuit current ?
(a) Resistance only
(b) Inductance only
(c) Capacitance only
(d) Inductance and capacitance
Ans: b
41. A crack in the magnetic path of an inductor will result in
(a) unchanged inductance
(b) increased inductance
(c) zero inductance
(d) reduced inductance
Ans: d
42. A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by
(a) variation in coil current
(b) variation in voltage to the coil
(c) change of number of turns of coil
(d) the resistance of magnetic path
Ans: b
43. A moving magnetic field will produce the same effect as a conductor that is moving.
(a) Yes
(b) No
Ans:
44. The polarity of the induced voltage can be determined by using the left-hand generator rule.
(a) Yes
(b) No
Ans: a
45. Increasing the field or increasing the current will decrease the force on the conductor.
(a) Yes
(b) No
Ans: b
46. Reversing the field or the current will reverse the force on the conductor.
(a) Yes
(b) No
Ans: a
47. When a conductor moves in the field, so that it makes an angle 8 with the lines of flux, the force F is given as : F = Bl sin2 0.
(a) Yes
(b) No
Ans: b
48. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts when the current in the circuit changes at the rate of unit weber turns.
(a) Yes
(b) No
Ans: b
Magnetism & Electromagnet
4.1. Tesla is a unit of
(a) field strength
(b) inductance
(c) flux density
(d) flux
Ans: c
4.2. A permeable substance is one
(a) which is a good conductor
(6) which is a bad conductor
(c) which is a strong magnet
(d) through which the magnetic lines of force can pass very easily
Ans: d
4.3. The materials having low retentivity are suitable for making
(a) weak magnets
(b) temporary magnets
(c) permanent magnets
(d) none of the above
Ans: b
4.4. A magnetic field exists around
(a) iron
(b) copper
(c) aluminium
(d) moving charges
Ans: d
4.7. Ferrites are materials.
(a) Paramagnetic
(b) diamagnetic
(c) ferromagnetic
(d) none of the above
Ans: c
4.8. Air gap has_______Reluctance as compared to iron or steel path
(a) little
(b) lower
(c) higher
(d) zero
Ans: b
4.9. The direction of magnetic lines of force is
(a) from south pole to north pole
(b) from north pole to south pole
(c) from one end of the magnet to another
(d) none of the above
Ans: b
4.10. Which of the following is a vector quantity ?
(a) Relative permeability
(b) Magnetic field intensity
(c) Flux density
(d) Magnetic potential
Ans: b
4.11. The two conductors of a transmission line carry equal current I in opposite directions. The force on each conductor is
(a) proportional to 7
(b) proportional to X
(c) proportional to distance between the conductors
(d) inversely proportional to I
Ans: b
4.12. A material which is slightly repelled by a magnetic field is known as
(a) ferromagnetic material
(b) diamagnetic material
(c) paramag>etic material
(d) conducting material
Ans: b
4.13. When an iron piece is placed in a magnetic field
(a) the magnetic lines of force will bend away from their usual paths in order to go away from the piece
(b) the magnetic lines of force will bend away from their usual paths in order to pass through the piece
(c) the magnetic field will not be affected
(d) the iron piece will break
Ans: b
4.14. Fleming's left hand rule is used to find
(a) direction of magnetic field due to current carrying conductor
(b) direction of flux in a solenoid
(c) direction of force on a current carrying conductor in a magnetic field
(d) polarity of a magnetic pole
Ans: c
4.15. The ratio of intensity of magnetisation to the magnetisation force is known as
(a) flux density
(b) susceptibility
(c) relative permeability
(d) none of the above
Ans: b
4.16. Magnetising steel is normals difficult because
(a) it corrodes easily
(6) it has high permeability
(c) it has high specific gravity
(d) it has low permeability
Ans: d
4.17. The left hand rule correlates to
(a) current, induced e.m.f. and direction of force on a conductor
(b) magnetic field, electric field and direction of force on a conductor
(c) self induction, mutual induction and direction of force on a conductor
(d) current, magnetic field and direction of force on a conductor
Ans: d
4.18. The unit of relative permeability is
(a) Henry/metre
(b) Henry
(c) Henry/sq. m
(d) it is dimensionless
Ans: d
4.19. A conductor of length L has current I passing through it, when it is placed parallel to a magnetic field. The force experienced by the conductor will be
(a) zero
(b) BLI
(c) B2LI
(d) BLI2
Ans: a
4.20. The force between two long parallel conductors is inversely proportional to
(a) radius of conductors
(b) current in one conductor
(c) product of current in two conductors
(d) distance between the conductors
Ans: d
4.21. Materials subjected to rapid reversal of magnetism should have
(a) large area of B-H loop
(b) high permeability and low hysteresis loss
(c) high co-ercivity and high retentivity
(d) high co-ercivity and low density
Ans: b
4.22. Indicate which of the following material does not retain magnetism permanently.
(a) Soft iron
(b) Stainless steel
(e) Hardened steel
(d) None of the above
Ans: a
4.23. The main constituent of permalloy is
(a) cobalt
(b) chromium
(c) nickel
(d) tungsten
Ans: c
4.24. The use of permanent magnets is not made in
(a) magnetoes
(6) energy meters
(c) transformers
(d) loud-speakers
Ans: c
4.25. Paramagnetic materials have relative permeability
(a) slightly less than unity
(b) equal to unity
(c) slightly more than unity
(d) equal to that ferromagnetic materials
Ans: c
4.26. Degaussing is the process of
(a) removal of magnetic impurities
(b) removing gases from the materials
(c) remagnetising metallic parts
(d) demagnetising metallic parts
Ans:
4.27. Substances which have permeability less than the permeability of free space are known as
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) bipolar
Ans: c
4.28. Two infinitely long parallel conductors in vacuum and' separated 1 metre between centres then a current of 1 ampere flows through each conductor, produce on each other a force of
(a) 2 x 1(T2 N/m)
(b) 2 x KT3 N/m
(c) 2 x 10"5 N/m
(d) 2x 1(T7 N/m)
Ans: d
4.29. In the left hand rule, forefinger always represents
(a) voltage
(b) current
(c) magnetic field
(d) direction of force on the conductor
Ans: c
4.30. Which of the following is a ferromagnetic material ?
(a) Tungsten
(b) Aluminium
(c) Copper
(d) Nickel
Ans: d
4.31. Ferrites are a sub-group of
(a) non-magnetic materials
(6) ferro-magnetic materials
(c) paramagnetic materials
(d) ferri-magnetic materials
Ans: d
4.32. Gilbert is a unit of
(a) electromotive force
(6) magnetomotive force
(c) conductance
(d) permittivity
Ans: b
4.33. The working of a meter is based on the use of a permanent magnet. In order to protect the meter functioning from stray magnetic fields
(a) meter is surrounded by strong magnetic fields
(b) a soft iron shielding is used
(c) a plastic shielding is provided
(d) a shielding of anon-magnetic material is used
Ans: b
4.34. Reciprocal of permeability is
(a) reluctivity
(b) susceptibility
(c) permittivity
(d) conductance
Ans: a
4.35. The relative permeability is less than unity is case of
(a) ferromagnetic materials
(b) ferrites
(c) non-ferrous materials
(d) diamagnetic materials
Ans: d
4.36. Which of the following is the unit of magnetic flux density ?
(a) Weber
(b) lumens
(c) tesla
(d) none of the above
Ans: c
4.37. The magnetism left in the iron after exciting field has been removed is known as
(a) permeance
(b) residual magnetism
(c) susceptance
(d) reluctance
Ans: b
4.38. Which of the following is not a unit of flux?
(a) Maxwell
(b) Tesla
(c) Weber
(d) All of the above
Ans: b
4.39. Which of the following is expected to have the maximum permeability ?
(a) Brass
(b) Copper
(c) Zinc
(d) Ebonite
Ans: d
4.40. One tesla is equal to
(a) 1 Wb/mm2
(b) 1 Wb/m
(c) 1 Wb/m2
(d) 1 mWb/m2
Ans: c
4.42. Out of the following statements, concerning an electric field, which statement is not true ?
(a) The electric intensity is a vector quantity
(b) The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point
(c) An electric field is defined as a point in space at which an electric charge would experienc* a force
(d) Unit field intensity in the exertion of a force of one newton on a charge of one coulomb
Ans: b
4.43. When a magnet is in motion relative to a coil the induced e.m.f. does not depend upon
(a) resistance of the coil
(b) motion of the magnet
(c) number of turns of the coil
(d) pole strength of the magnet
Ans: a
4.44. One Maxwell is equal to
(a) 10 webers
(b) 10 webers
(c) 10 webers
(d) 10 webers
Ans: d
4.46. When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the centre of the circle
(a) will be zero
(b) will be infinite
(c) will depend on the amount of e.m.f. applied
(d) will depend on the radius of the circle
Ans: d
4.47. Susceptibility is positive for
(a) non-magnetic substances
(b) diamagnetic substances
(c) ferromagnetic substances
(d) none of the above
Ans: c
4.48. Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per metre of length of each conductor will be
(a) 100 N
(b) 10 N
(c) 1 N
(d) 0.1 N
Ans: d
4.49. A 300 mm long conductor is carrying a current of 10 A and is situated at right angles to a magnetic field having a flux density of 0.8 T ; the force on the conductor will be
(a) 240 N
(6) 24 N
(c) 2.4 N
(d) 0.24 N
Ans: c
4.50. A 200 turn coil having an axial length of 30 mm and a radius of 10 mm is pivoted in a magnetic field having a flux density of 0.8 T. If the coil carries a current of 0.5 A, the torque acting on the coil will be
(a) 4.8 N-m
(b) 0.48 N-m
(e) 0.048 N-m
(d) 0.0048 N-m
[Hint. Torque = 2BIlNr N-m]
Ans: c
4.51. The electromagnet has 50 turns and a current of 1A flows through the coil. If the length of the magnet circuit is 200 mm, what is the magnetic field strength ?
(a) 2500 AT/m
(b) 250 AT/m
(c) 25 AT/m
(d) 2.5 AT/m
Ans: b
4.52. What is the magnitude and the direction of force per 1.1m length of a pair of conductors of a direct current linecarrying 10 amperes and spaced 100 mm apart ?
(a) 22 x 10"8 N
(b) 22 x 10"7 N
(c) 22 x 10-6 N
(d) 22 x 10"5 N
Ans: d
4.53. A square cross-sectional magnet has a pole strength of 1 x 10 Wb and cross sectional area of 20 mm x 20 mm. What is the strength at a distance of 100 mm from the unit pole in air ?
(a) 63.38 N/Wb
(b) 633.8 N/Wb
(c) 6338 N/Wb
(d) 63380 N/Wb
Ans: c
4.56.. The unit of flux is the same as that of
(a) reluctance
(b) resistance
(c) permeance
(d) pole strength
Ans: d
4.57. Unit for quantity of electricity is
(a) ampere-hour
(b) watt
(c) joule
(d) coulomb
Ans: d
4.58. The Biot-savart's law is a general modification of
(a) Kirchhoffs law
(b) Lenz's law
(c) Ampere's law
(d) Faraday's laws
Ans: c
4.61. The most effective and quickest may of making a magnet from soft iron is by
(a) placing it inside a coil carrying current
(b) induction
(c) the use of permanent magnet
(d) rubbing with another magnet
Ans: a
4.62. The commonly used material for shielding or screening magnetism is
(a) copper
(b) aluminium
(c) soft iron
(d) brass
Ans: c
4.63. If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity
(a) less than that of disc but in opposite direction
(b) equal to that of disc and in the same direction
(c) equal to that of disc and in the opposite direction
(d) less than that of disc and in the same direction
Ans: d
4.64. A permanent magnet
(a) attracts some substances and repels others
(b) attracts all paramagnetic substances and repels others
(c) attracts only ferromagnetic substances
(d) attracts ferromagnetic substances and repels all others
Ans: a
4.65. The retentivity (a property) of material is useful for the construction of
(a) permanent magnets
(b) transformers
(c) non-magnetic substances
(d) electromagnets
Ans: a
4.66. The relative permeability of materials is not constant.
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) insulating
Ans: c
4.67. The materials are a bit inferior conductors of magnetic flux than air.
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) dielectric
Ans: c
4.68. Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials.
(a) circular
(b) triangular
(c) rectangular
(d) none of the above
Ans: c
4.69. A rectangular magnet of magnetic moment M is cut into two piece of same length, the magnetic moment of each piece will be
(a) M
(6) M/2
(c) 2 M
(d) M/4
Ans: b
4.70. A keeper is used to
(a) change the direction of magnetic lines
(b) amplify flux
(c) restore lost flux
(d) provide a closed path for flux
Ans: d
4.71. Magnetic moment is a
(a) pole strength
(6) universal constant
(c) scalar quantity
(d) vector quantity
Ans: d
4.72. The change of cross-sectional area of conductor in magnetic field will affect
(a) reluctance of conductor
(b) resistance of conductor
(c) (a) and (b) b >th in the same way
(d) none of the above
Ans: c
4.73. The uniform magnetic field is
(a) the field of a set of parallel conductors
(b) the field of a single conductor
(c) the field in which all lines of magnetic flux are parallel and equidistant
(d) none of the above
Ans: c
4.74. The magneto-motive force is
(a) the voltage across the two ends of exciting coil
(b) the flow of an electric current
(c) the sum of all currents embraced by one line of magnetic field
(d) the passage of magnetic field through an exciting coil
Ans: c
4.75. What will be the current passing through the ring shaped air cored coil when number of turns is 800 and ampere turns are 3200 ?
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b
4.76. What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m ?
(a) 2 AT
(b) 4 AT
(c) 6 AT
(d) 10 AT
Ans: b
4.77. Which of the following statements is correct ?
(a) The magnetic flux inside an exciting coil is lower than its outside surface
(6) The magnetic flux inside an exciting coil is zero
(e) The magnetic flux inside the exciting coil is greater than its outside surface
(d) The magnetic flux inside the exciting coil is same as on its outside surface
Ans: d
4.78. A certain amount of current flows through a ring-shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil ?
(a) Decreases
(b) Increases
(c) Remains same
(d) First increases and then decreases depending on the depth of iron insertion
Ans: b
4.79. The magnetic reluctance of a material
(a) decreases with increasing cross sectional area of material
(6) increases with increasing cross-sectional area of material
(c) does not vary with increasing cross-sectional area of material
(d) any of the above
Ans: a
4.80. The initial permeability of an iron rod is
(a) the highest permeability of the iron rod
(b) the lowest permeability of the iron rod
(c) the permeability at the end of the iron rod
(d) the permeability almost in non-magnetised state
Ans: d
4.82. How does the magnetic compass needle behave in a magnetic field ?
(a) It assures a position right angle to magnetic field
(b) It starts rotating
(c) It assures a position which follows a line of magnetic flux
(d) None of the above
Ans: c
4.83. In a simple magnetic field the strength of magnet flux
(a) is constant and has same value in energy part of the magnetic field
(6) increases continuously from initial value to final value
(c) decreases continuously from initial value to final value
(d) first increases and then decreases till it becomes zero
Ans: d
4.84. The stray line of magnetic flux is defined as
(a) a line vertical to the flux lines
(b) the mean length of a ring shaped coil
(c) a line of magnetic flux in a non-uniform field
(d) a line of magnetic flux which does not follow the designed path
Ans: d
4.85. The bar magnet has
(a) the dipole moment
(b) monopole moment
(c) (a) and (b) both
(d) none of the above
Ans: a
4.86. Which of the following materials are diamagnetic?
(a) Silver
(b) Copper
(c) Silver and copper
(d) Iron
Ans: c
4.87. Which of the following type of materials are not very important for engineering applications ?
(a) Ferromagnetic
(b) Paramagnetic
(c) Diamagnetic
(d) None of the above
Ans: c
4.88. The susceptibility of paramagnetic materials generally lies between
(a) KT3 and 1CT6
(b) 1CT3 and 1CT7
(c) KT4 and KT8
(d) 10"2 and KT5
Ans: a
4.89. For which of the following materials the saturation value is the highest ?
(a) Ferromagnetic materials
(6) Paramagnetic materials
(c) Diamagnetic materials
(d) Ferrites
Ans: d
4.90. The magnetic materials exhibit the property of magnetisation because of
(a) orbital motion of electrons
(b) spin of electrons
(c) spin of nucleus
(d) either of these
(e) all of the above
Ans: c
4.91. For which of the following materials the net magnetic moment should be zero ?
(a) Diamagnetic materials
(b) Ferrimagnetic materials
(c) Antiferromagnetic materials
(d) Antiferrimagnetic materials
Ans: c
4.92. The attraction capacity of electromagnet will increase if the
(a) core length increases i
(b) core area increases
(c) flux density decreases
(d) flux density increases
Ans: d
4.93. Which of the following statements is correct ?
(a) The conductivity of ferrites is better than ferromagnetic materials
(b) The conductivity of ferromagnetic materials is better than ferrites
(c) The conductivity of ferrites is very high
(d) The conductivity of ferrites is same as that of ferromagnetic materials
Ans: a
4.96. Temporary magnets are used in
(a) loud-speakers
(b) generators
(c) motors
(d) all of the above
Ans: d
4.97. Main causes of noisy solenoid are
(a) strong tendency of fan out of lami-nations at the end caused by repul¬sion among magnetic lines of force
(b) uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
(c) both of above
(d) none of the above
Ans: c
4.99. Strength of an electromagnet can be increased by
(a) increasing the cross-sectional area
(b) increasing the number of turns
(c) increasing current supply
(d) all above methods
Ans:
4.100. Core of an electromagnet should have
(a) low coercivity
(6) high susceptibility
(c) both of the above
(d) none of the above
Ans: c
4.101. Magnetism of a magnet can be destroyed by
(a) heating
(b) hammering
(c) by inductive action of another magnet
(d) by all above methods
Ans: d
Magnetic Circuit
1. An air gap is usually inserted in magnetic circuits to
(a) increase m.m.f.
(b) increase the flux
(c) prevent saturation
(d) none of the above
Ans: c
2. The relative permeability of a ferromagnetic material is
(a) less than one
(b) more than one
(c) more than 10
(d) more than 100 or 1000
Ans: d
3. The unit of magnetic flux is
(a) henry
(b) weber
(c) ampereturn/weber
(d) ampere/metre
Ans: b
4. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
(a) resistance
(b) resistivity
(c) conductivity
(d) conductance
Ans: c
5. Point out the wrong statement.
Magnetic leakage is undesirable in electric machines because it
(a) lowers their power efficiency
(b) increases their cost of manufacture
(c) leads to their increased weight
(d) produces fringing
Ans: a
6. Relative permeability of vacuum is
(a) 1
(b) 1 H/m
(c) 1/4JI
(d) 4n x 10-' H/m
Ans: a
7. Permanent magnets are normally made of
(a) alnico alloys
(b) aluminium
(c) cast iron
(d) wrought iron
Ans: a
8. Energy stored by a coil is doubled when its current is increased by percent.
(a) 25
(b) 50
(c)41.4
(d) 100
Ans: c
9. Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss.
(a) high, high
(b) low, high
(c) high, low
(d) low, low
Ans: c
10. The rate of rise of current through an inductive coil is maximum
(a) at 63.2% of its maximum steady value
(b) at the start of the current flow
(c) after one time constant
(d) near the final maximum value of current
Ans: b
11. When both the inductance and resistance of a coil are doubled the value of
(a) time constant remains unchanged
(b) initial rate of rise of current is doubled
(c) final steady current is doubled
(d) time constant is halved
Ans: a
12. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is_______Vs
(a) 50
(b) 20
(c) 0.05
(d) 500
Ans: b
13. A material for good magnetic memory should have
(a) low hysteresis loss
(b) high permeability
(c) low retentivity
(d) high retentivity
Ans: d
14. Conductivity is analogous to
(a) retentivity
(b) resistivity
(c) permeability
(d) inductance
Ans: c
15. In a magnetic material hysteresis loss takes place primarily due to
(a) rapid reversals of its magnetisation
(b) flux density lagging behind magnetising force
(c) molecular friction
(d) it high retentivity
Ans: d
16. Those materials are well suited for making permanent magnets which have______retentivity and _______coercivity.
(a) low, high
(b) high, high
(c) high, low
(d) low, low
Ans: b
17. If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be
(a) zero
(b) small
(c) large
(d) none of the above
Ans: c
18. Hard steel is suitable for making permanent magnets because
(a) it has good residual magnetism
(b) its hysteresis loop has large area
(c) its mechanical strength is high
(d) its mechanical strength is low
Ans: a
19. Silicon steel is used in electrical machines because it has
(a) low co-ercivity
(b) low retentivity
(c) low hysteresis loss
(d) high co-ercivity
Ans: c
20. Conductance is analogous to
(a) permeance
(b) reluctance
(c) flux
(d) inductance
Ans: a
21. The property of a material which opposes the creation of magnetic flux in it is known as
(a) reluctivity
(b) magnetomotive force
(c) permeance
(d) reluctance
Ans: d
22. The unit of retentivity is
(a) weber
(b) weber/sq. m
(c) ampere turn/metre
(d) ampere turn
Ans: b
23. Reciprocal of reluctance is
(a) reluctivity
(b) permeance
(c) permeability
(d) susceptibility
Ans: b
24. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ?
(a) E.m.f.
(b) Current
(c) Current density
(d) Conductivity
Ans: b
25. The unit of reluctance is
(a) metre/henry
(b) henry/metre
(c) henry
(d) 1/henry
Ans: d
26. A ferrite core has less eddy current loss than an iron core because
(a) ferrites have high resistance
(b) ferrites are magnetic
(c) ferrites have low permeability
(d) ferrites have high hysteresis
Ans: d
27. Hysteresis loss least depends on
(a) volume of material
(b) frequency
(c) steinmetz co-efficient of material
(d) ambient temperature
Ans: d
28. Laminated cores, in electrical machines, are used to reduce
(a) copper loss
(b) eddy current loss
(c) hysteresis loss
(d) all of the above
Ans: b
AC Fundamental
1. A sine wave has a frequency of 50 Hz. Its angular frequency is _______ radian/second.
(a) 100 n
(b) 50 jt
(c) 25 jt
(d) 5 n
Ans: a
2. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15
Ans: c
3. The period of a wave is
(a) the same as frequency
(6) time required to complete one cycle
(c) expressed in amperes
(d) none of the above
Ans: b
4. The form factor is the ratio of
(a) peak value to r.m.s. value
(6) r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b
5. The period of a sine wave is _____ seconds.
Its frequency is
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz
Ans: d
6. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to
(a) average voltage
(b) r.m.s. voltage
(c) peak voltage
(d) none of the above
Ans: b
7. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
(d) not a sinusoid
Ans: a
8. The peak value of a sine wave is 200 V. Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a
9. If two sine waves of the same frequency have a phase difference of JT radians, then
(a) both will reach their minimum values at the same instant
(b) both will reach their maximum values at the same instant
(c) when one wave reaches its maximum value, the other will reach its minimum value
(d) none of the above
Ans: c
10. The voltage of domestic supply is 220V. This figure represents
(a) mean value
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a
11. Two waves of the same frequency have opposite phase when the phase angle between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b
12. The power consumed in a circuit element will be least when the phase difference between the current and
voltage is
(a) 180"
(b) 90°
(c) 60°
(d) 0°
Ans: b
13. The r.m.s. value and mean value is the same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c
14. For the same peak value which of the following wave will 'have the highest r.m.s. value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a
15. For the same peak value, which of the following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a
16. For a sine wave with peak value Imax the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b
17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c
18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c
19. For a sine wave with peak value Emax______8.30. the average value is
(a) 0.636 Emax
(b) 0.707 Emax
(c) 0.434 EWc
(d) lAUEmax
Ans: a
20. For a frequency of 200 Hz, the time period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b
21. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that
(a) both waves must have same frequency
(b) both waves must have identical peak values
(c) both waves must have zero value at the same time
(d) none of the above
Ans: a
22. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c
23. Capacitive reactance is more when
(a) capacitance is less and frequency of supply is less
(b) capacitance is less and frequency of supply is more
(c) capacitance is more and frequency of supply is less
(d) capacitance is more and frequency of supply is more
Ans: a
24. In a series resonant circuit, the impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
(d) none of the above
Ans: a
25. Power factor of an electrical circuit is equal to
(a) R/Z
(b) cosine of phase angle difference between current and voltage
(c) kW/kVA
(d) ratio of useful current to total current Iw/I
(e) all above
Ans: e
26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the inductive load
(c) far away from the inductive load
(d) any where
Ans: b
27. Poor power factor
(a) reduces load handling capability of electrical system
(b) results in more power losses in the electrical system
(c) overloads alternators, transformers and distribution lines
(d) results in more voltage drop in the line
(e) results in all above
Ans: e
28. Capacitors for power factor correction are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d
29. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value
(a) will change the maximum value of current at resonance
(6) will change the resonance frequency
(c) will change the impedance at resonance frequency
(d) will increase the selectivity of the circuit
Ans: d
30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle
(d) none of the above
Ans: c
31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c
32. Inductance of a coil Varies
(a) directly as the cross-sectional area of magnetic core
(b) directly as square of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e
33. All the rules and laws of D.C. circuit also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c
34. Time constant of an inductive circuit
(a) increases with increase of inductance and decrease of resistance
(b) increases with the increase of inductance and the increase of resistance
(c) increases with decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a
35. Power factor of an inductive circuit is usually improved by connecting capacitor to it in
(a) parallel
(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a
36. In a highly capacitive circuit the
(a) apparent power is equal to the actual power
(b) reactive power is more than the apparent power
(c) reactive power is more than the actual powetf
(d) actual power is more than its reactive power
Ans: c
37. Power factor of the following circuit will be zero
(a) resistance
(b) inductance
(c) capacitance
(d) both (b) and (c)
Ans: d
38. Power factor of the following circuit will be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c
39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the capacities of generators, lines and transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d
40. The time constant of the capacitance circuit is defined as the time during which voltage
(a) falls to 36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
Ans: c
41. In a loss-free R-L-C circuit the transient current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c
42. The r.m.s. value of alternating current is given by steady (D.C.) current which when flowing through a given circuit for a given time produces
(a) the more heat than produced by A.C. when flowing through the same circuit
(b) the same heat as produced by A.C. when flowing through the same circuit
(c) the less heat than produced by A.C. flowing through the same circuit
(d) none of the above
Ans: b
43. The square waveform of current has following relation between r.m.s. value and average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than average value
(c) r.m.s. value of current is less than average value
(d) none of the above
Ans: a
44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d) R-L-C circuit
Ans: d
45. The transient currents are associated with the
(a) changes in the stored energy in the inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a
46. The power factor at resonance in R-L- C parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d
47. In the case of an unsymmetrical alternating current the average value must always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d
48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d) current is in phase with the voltage
Ans: d
49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by 90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b
50. In a circuit containing R, L and C, power loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c
51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply frequency
(c) increases with the increase in supply frequency
(d) becomes zero with the increase in supply frequency
Ans: c
52. In any A.C. circuit always
(a) apparent power is more than actual power
(b) reactive power is more than apparent power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a
53. Which of the following circuit component opposes the change in the circuit voltage ?
(a) Inductance
(b) Capacitance
(c) Conductance
(d) Resistance
Ans:
54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a
55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d
56. Pure inductive circuit takes power from the A.C. line when
(a) applied voltage decreases but cur¬rent increases
(b) applied voltage increases but cur¬rent decreases
(c) both applied voltage and current increase
(d) both applied voltage and current decrease
Ans: a
57. Time constant of a circuit is the time in seconds taken after the application of voltage to each
(a) 25% of maximum value
(b) 50% of maximum value
(c) 63% of maximum value
(d) 90% of the maximum value
Ans: c
58. Time constant of an inductive circuit
(a) increases with increase of inductance and decrease of resistance
(b) increases with the increase of inductance and the increase of resistance
(c) increases with the decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a
59. Time constant of a capacitive circuit
(a) increases with the decrease of capacitance and decrease of resistance
(b) increases with the decrease of capacitance and increase of resis¬tance
(c) increases with the increase of capacitance and decrease of resis¬tance
(d) increase with increase of capacitance and increase of resis¬tance
Ans: d
60. Magnitude of current at resonance in R-L-C circuit
(a) depends upon the magnitude of R
(b) depends upon the magnitude of L
(c) depends upon the magnitude of C
(d) depends upon the magnitude of R, LandC
Ans: a
61. In a R-L-C circuit
(a) power is consumed in resistance and is equal to I R
(b) exchange of power takes place between inductor and supply line
(c) exchange of power takes place between capacitor and supply line
(d) exchange of power does not take place between resistance and the supply line
(e) all above are correct
Ans: e
62. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of
(a) R only
(b) L only
(c) C only
(d) L or C
(e) R,L or C
Ans: d
63. In a series L-C circuit at the resonant frequency the
(a) current is maximum
(b) current is minimum
(c) impedance is maximum
(d) voltage across C is minimum
Ans: a
64. The time constant of a series R-C circuit is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c
65. If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be
(a) 0.001 s
(b) 0.1 s
(c) 10 s
(d) 100 s
Ans: b
66. Which of the following coil will have large resonant frequency ?
(a) A coil with large resistance
(b) A coil with low resistance
(c) A coil with large distributed capacitance
(d) A coil with low distributed capacitance
Ans: c
67. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?
(a) 42.42 sin 3141
(b) 60 sin 25 t
(c) 30 sin 50 t
(d) 84.84 sin 25 t
Ans: a
68. The safest value of current the human body can carry for more than 3 second is
(a) 4 mA
(b) 9 mA
(c) 15 mA
(d) 25 mA
Ans: b
69. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W.
This consumption can be attributed to
(a) the big size of the inductor
(b) the reactance of the inductor
(c) the current flowing in the inductor
(d) the statement given is false
Ans: d
70. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
(a) 12 kW
(b) 22 kW
(c) 32 kW
(d) 64 kW
Ans: c
71. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of
(a) iron loss in core
(b) skin effect
(c) increase in temperature
(d) capacitive effect between adjacent coil turns
Ans: a
72. In an AC. circuit, a low value of kVAR compared with kW indicates
(a) low efficiency
(b) high power factor
(c) unity power factor
(d) maximum load current
Ans: b
73. In AC. circuits, laminated iron is invariably used in order to
(a) reduce eddy current loss
(b) increase heat radiation
(c) make assembly cheap and easier
(d) reduce circuit permeability
Ans: a
74. The ratio of active power to apparent power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c
75. All definitions of power factor of a series R-L-C circuit are correct except
(a) ratio of net reactance and impedance
(b) ratio of kW and kVA
(c) ratio of J and Z
(d) ratio of W and VA
Ans: a
76. The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is
(a) 4 kVAR
(b) 6 kVAR
(c) 8 kVAR
(d) 16 kVAR
Ans: b
77. What will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value ?
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Ans: c
78. The purpose of a parallel circuit resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b
79. In an A.C. circuit power is dissipated in
(a) resistance only
(b) inductance only
(c) capacitance only
(d) none of the above
Ans: a
80. In a parallel R-C circuit, the current always______the applied voltage
(a) lags
(b) leads
(c) remains in phase with
(d) none of the above
Ans: b
81. At very low frequencies a series R-C circuit behaves as almost purely
(a) resistive
(b) inductive
(c) capacitive
(d) none of the above
Ans: c
82. Skin effect occurs when a conductor carries current at _____ frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d
83. At ______ frequencies the parallel R-L circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d
84. In a sine wave the slope is constant
(a) between 0° and 90°
(b) between 90° and 180°
(c) between 180° and 270°
(d) no where
Ans: d
85. The power is measured in terms of decibles in case of
(a) electronic equipment
(b) transformers
(c) current transformers
(d) auto transformers
Ans: a
86. Capacitive susceptance is a measure of
(a) reactive power in a circuit
(b) the extent of neutralisation of reactive power in a circuit
(c) a purely capacitive circuit's ability to pass current
(d) a purely capacitive circuit's ability to resist the flow of current
Ans: c
87. Which of the following statements pertains to resistors only ?
(a) can dissipate considerable amount of power
(6) can act as energy storage devices
(c) connecting them in parallel in¬creases the total value
(d) oppose sudden changes in voltage
Ans: a
88. Which of the following refers to a parallel circuit ?
(a) The current through each element is same
(b) The voltage across element is in proportion to it's resistance value
(c) The equivalent resistance is greater than any one of the resistors
(d) The current through any one element is less than the source current
Ans: d
89. Aphasoris
(a) a line which represents the mag¬nitude and phase of an alternating quantity
(b) a line representing the magnitude and direction of an alternating quantity
(c) a coloured tag or band for distinction between different phases of a 3-phase supply
(d) an instrument used for measuring phases of an unbalanced 3-phase load
Ans: a
89. A parallel AC. circuit in resonance will
(a) have a high voltage developed across each inductive and capacitive section
(b) have a high impedance
(c) act like a resistor of low value
(d) have current in each section equal to the line current
Ans: b
90. Wire-wound resistors are unsuitable for use at high frequencies because they
(a) create more electrical noise
(b) are likely to melt under excessive eddy current heat
(c) consume more power
(d) exhibit unwanted inductive and capacitive effects
Ans: d
91. The inductance of a coil can be increased by
(a) increasing core length
(b) decreasing the number of turns
(c) decreasing the diameter of the former
(d) choosing core material having high relative permeability
Ans: d
92. In a three-phase supply floating neutral is undesirable because it way give rise to
(a) high voltage across the load
(b) low voltage across the load
(c) unequal line voltages across the load
Ans: c
93. Which of the following waves has the highest value of peak factor ?
(a) Square wave
(b) Sine wave
(c) Half wave rectified sine wave
(d) Triangular wave
Ans: c
94. The frequency of domestic power supply in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d
95. The r.m.s. value of half wave rectified sine wave is 200 V. The r.m.s. value of full wave rectified AC. will be
(a) 282.8 V
(b) 141.4 V
(c) 111 V
(d) 100 V
Ans: a
96. The r.m.s. value of pure cosine function is
(a) 0.5 of peak value
(b) 0.707 of peak value
(c) same as peak value
(d) zero
Ans: b
97. Ohm is unit of all of the following except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d) capacitance
Ans: d
98. The series ;nd parallel resonance on L-C circui' differs in that
(a) series resistance needs a low-resistance ource for sharp rise in current
(b) series resonance needs a high-resistance source for sharp increase in current
(c) parallel resonance needs a low-resistance source for a sharp in¬crease in impedance
(d) parallel resonance needs a low-resistance source for a sharp rise in line current
Ans: a
99. The phasors for which of the following pair are 180° out of phase for VL, VC and VR?
(a) Vc and VR
(b) VL and VR
(c) Vc and VL
(d) none of the above
Ans: c
100. The frequency of an alternating current is
(a) the speed with which the alternator runs
(b) the number of cycles generated in one minute
(c) the number of waves passing through a point in one second
(d) the number of electrons passing through a point in one second
Ans: c
101. A pure capacitor connected across an A.C. voltage consumed 50 W. This is due to
(a) the capacitive reactance in ohms
(b) the current flowing in capacitor
(c) the size of the capacitor being quite big
(d) the statement is incorrect
Ans: d
102. The power factor of a D.C. circuit is always
(a) less than unity
(b) unity
(c) greater than unity
(d) zero
Ans: b
103. The product of apparent power and cosine of the phase angle between circuit voltage and current is
(a) true power
(b) reactive power
(c) volt-amperes
(d) instantaneous power
Ans: a
104. The equation of 50 Hz current sine wave having r.m.s. value of 60 A is
(a) 60 sin 25 t
(b) 60 sin 50 t
(c) 84.84 sin 3141
(d) 42.42 sin 314 t
Ans: c
105. An A.C. voltage is impressed across a pure resistance of 3.5 ohms in parallel with a pure inductance of impedance of 3.5 ohms,
(a) the current through the resistance is more
(b) the current through the resistance is less
(c) both resistance and inductance carry equal currents
(d) none of the above
Ans: c
106. In a pure inductive circuit if the supply frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times as high
(d) be reduced to one fourth
Ans: b
107. In a pure capacitive circuit if the supply frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times at high
(d) be reduced to one fourth
Ans: a
108. When an alternating current passes through an ohmic resistance the electrical power converted into heat is
(a) apparent power
(b) true power
(c) reactive power
(d) none of the above
Ans: b
109. In each of the three coils of a three phase generator, an alternating voltage having an r.m.s. value of 220 V is induced. Which of the following values is indicated by the voltmeters ?
(a) 220 V
(b) 220V3V
(c) 220/V3 V
(d) none of the above
Ans: a
Industrial drives & control
1. The selection of an electric motor for any application depends on which of the following factors ?
(a) Electrical characteristics
(b) Mechanical characteristics
(c) Size and rating of motors
(d) Cost
(e) All of the above
Ans: e
2. For a particular application the type of electric-and control gear are determined by which of the following considerations ?
(a) Starting torque
(b) Conditions of environment
(c) Limitation on starting current
(d) Speed control range and its nature
(e) All of the above
Ans: e
3. Which of the following motors is preferred for traction work ?
(a) Universal motor
(b) D.C. series motor
(c) Synchronous motor
(d) Three-phase induction motor
Ans:
4 Which of the following motors always starts on load ?
(a) Conveyor motor
(b) Floor mill motor
(c) Fan motor
(d) All of the above
Ans: d
5 is preferred for automatic drives.
(a) Squirrel cage induction motor
(b) Synchronous motors
(c) Ward-Leonard controlled D.C. motors
(d) Any of the above
Ans: c
6. When the load is above _____ a synchronous motor is found to be more economical.
(a) 2 kW
(b) 20 kW
(c) 50 kW
(d) 100 kW
Ans: d
7. The load cycle for a motor driving a power press will be
(a) variable load
(b) continuous
(c) continuous but periodical
(d) intermittent and variable load
Ans: d
8. Light duty cranes are used in which of the following ?
(a) Power houses
(b) Pumping stations
(c) Automobile workshops
(d) All of the above
Ans: d
9. While selecting an electric motor for a floor mill, which electrical characteristics will be of least significance ?
(a) Running characteristics
(b) Starting characteristics
(c) Efficiency
(d) Braking
Ans: d
10. Which of the following motors are pre-ferred for overhead travelling cranes ?
(a) Slow speed motors
(b) Continuous duty motors
(c) Short time rated motors
(d) None of the above
Ans: c
11 is preferred for synthetic fibre mills.
(a) Synchronous motor
(b) Reluctance motor
(c) Series motor
(d) Shunt motor
Ans: b
12. Ward-Leonard controlled D.C. drives are generally used for ______ excavators.
(a) Light duty
(b) Medium duty
(c) Heavy duty
(d) All of the above
Ans: c
13. Which of the following motors is used for elevators ?
(a) Induction motor
(b) Synchronous motor
(c) Capacitor start single phase motor
(d) Any of the above
Ans: a
14. Which part of a motor needs maximum attention for maintenance ?
(a) Frame
(b) Rearing
(c) Stator winding
(d) Rotor winding
Ans: b
15 need frequent starting and stopping of electric motors,
(a) Paper mills
(b) Grinding mills
(c) Air-conditioners
(d) Lifts and hoists
Ans: d
16. Which feature, while selecting a.motor for centrifugal pump, will be of least significance ?
(a) Starting characteristics
(b) Operating speed
(c) Horse power
(d) Speed control
Ans: d
17. _______ motor is a constant speed motor.
(a) Synchronous motor
(b) Schrage motor
(c) Induction motor
(d) Universal motor
Ans: a
18. The starting torque in case of centrifugal pumps is generally
(a) less than running torque
(b) same as running torque
(c) slightly more than running torque
(d) double the running torque
Ans: a
19. Which of the following motors are best for the rolling mills ?
(a) Single phase motors
(b) Squirrel cage induction motors
(c) Slip ring induction motors
(d) D.C. motors
Ans: d
20 is not a part of ball bearing ?
(a) Inner race
(b) Outer race
(c) Cage
(d) Bush
Ans: d
21. The starting torque of a D.C. motor is independent of which of the following?
(a) Flux
(b) Armature current
(c) Flux and armature current
(d) Speed
Ans: d
22. Rotor of a motor is usually supported on _______ bearings.
(a) ball or roller
(b) needle
(c) bush
(d) thrust
Ans: a
23. For which of the following applications D.C. motors are still preferred ?
(a) High efficiency operation
(b) Reversibility
(c) Variable speed drive
(d) High starting torque
Ans: c
24. In a paper mill where constant speed is required
(a) synchronous motors are preferred
(b) A.C. motors are preferred
(c) individual drive is preferred
(d) group drive is preferred
Ans: c
25. A reluctance motor
(a) is provided with slip rings
(b) requires starting gear
(c) has high cost
(d) is compact
Ans: d
26. The size of an excavator is usually expressed in terms of
(a) 'crowd' motion
(b) angle of swing
(c) cubic metres
(d) travel in metres
Ans: c
27. For blowers which of the following motor is preferred ?
(a) D.C. series motor
(b) D.C. shunt motor
(c) Squirrel cage induction motor
(d) Wound rotor induction motor
Ans: b
28. Belted slip ring induction motor is almost invariably used for
(a) water pumps
(b) jaw crushers
(c) centrifugal blowers
(d) none of the above
Ans: b
29. Which of the following is essentially needed while selecting a motor ?
(a) Pulley
(b) Starter
(c) Foundation pedal
(d) Bearings
Ans: b
30. Reluctance motor is a
(a) variable torque motor
(b) low torque variable speed motor
(c) self starting type synchronous motor
(d) low noise, slow speed motor
Ans: c
31 method of starting a three phase induction motor needs six terminals.
(a) Star-delta
(b) Resistance starting
(c) Auto-transformer
(d) None of the above
Ans: a
32. In ______ method of staging three phase induction motors the starting voltage is not reduced.
(a) auto-transformer
(b) star-delta
(c) slip ring
(d) any of the above
Ans: c
33. In jaw crushers a motor has to often start against ______ load.
(a) heavy
(b) medium
(c) normal
(d) low
Ans: a
34. For a motor-generator set which of the following motors will be preferred ?
(a) Synchronous motor
(b) Slip ring induction motor
(c) Pole changing induction motor
(d) Squirrel cage induction motor
Ans: a
35. Which of the following motors is usually preferred for kiln drives ?
(a) Cascade controlled A.C. motor
(b) Slip ring induction motor
(c) Three phase shunt wound com-mutator motor
(d) Any of the above
Ans: d
36. Heat control switches are used in
(a) transformers
(b) cooling ranges
(c) three phase induction motors
(d) single phase
Ans: b
37 has relatively wider range of speed control.
(a) Synchronous motor
(6) Ship ring induction motor
(c) Squirrel cage induction motor
(d) D.C. shunt motor
Ans: d
38. In squirrel cage induction motors which of the following methods of starting cannot be used ?
(a) Resistance in rotor circuit
(b) Resistance in stator circuit
(c) Auto-transformer starting
(d) Star-delta starting
Ans: a
39. In which of the following applications the load on motor changes in cyclic order ?
(a) Electric shovels
(b) Cranes
(c) Rolling mills
(d) All of the above
Ans: d
40. Flame proof motors are used in
(a) paper mills
(b) steel mills
(c) moist atmospheres
(d) explosive atmospheres
Ans: d
41. Which of the following machines has heavy fluctuation of load ?
(a) Printing machine
(b) Punching machine
(c) Planer
(d) Lathe
Ans: b
42. For derries and winches which of the following drives can be used ?
(a) Pole changing squirrel cage motors
(b) D.C. motors with Ward-leonard con-trol
(c) A.C. slip ring motors with variable resistance
(d) Any of the above
Ans: d
43. Battery operated scooter for braking uses
(a) plugging
(b) mechanical braking
(c) regenerative braking
(d) rheostatic braking
Ans: b
44 has least range of speed control.
(a) Slip ring induction motor
(b) Synchronous motor
(c) D.C. shunt motor
(d) Schrage motor
Ans: b
45 has the least value of starting torque to full load torque ratio.
(a) D.C. shunt motor
(b) D.C. series motor
(c) Squirrel cage induction motor
(d) Slip ring induction motor
Ans: c
46. In case of _______ speed control by injecting e.m.f. in the rotor circuit is possible,
(a) d.c. shunt motor
(b) schrage motor
(c) synchronous motor
(d) slip ring induction motor
Ans: d
47. A pony motor is used for the starting which of the following motors ?
(a) Squirel cage induction motor
(b) Schrage motor
(c) Synchronous motor
(d) None of the above
Ans: c
48. In ________ the speed can be varied by changing the position of brushes.
(a) slip ring motor
(b) schrage motor
(c) induction motor
(d) repulsion motor
Ans: b
49. In which of the following applications variable speed operation is preferred ?
(a) Exhaust fan
(b) Ceiling fan
(c) Refrigerator
(d) Water pump
Ans: b
50. Heavy duty cranes are used in
(a) ore handling plants
(b) steel plants
(c) heavy engineering workshops
(d) all of the above
Ans: d
51. The travelling speed of cranes varies from
(a) 20 to 30 m/s
(b) 10 to 15 m/s
(c) 5 to 10 m/s
(d) 1 to 2.5 m/s
Ans: d
52. Besides a constant speed a synchronous rotor possesses which of the following advantages ?
(a) Lower cost
(b) Better efficiency
(c) High power factor
(d) All of the above
Ans: c
53. By the use of which of the followingm D.C. can be obtained from AC. ?
(a) Silicon diodes
(b) Mercury arc rectifier
(c) Motor generator set
(d) Any of the above
Ans: d
54. Which of the following motors is preferred when quick speed reversal is the main consideration ?
(a) Squirrel cage induction motor
(b) Wound rotor induction motor
(e) Synchronous motor
(d) D.C. motor
Ans: d
55. Which ofthefollowing motors is preferred when smooth and precise speed control over a wide range is desired ?
(a) D.C. motor
(b) Squirrel cage induction motor
(c) Wound rotor induction motor
(d) Synchronous motor
Ans: a
56. For crane travel which of the following motors is normally used ?
(a) Synchronous motor
(b) D.C. differentially compound motor
(c) Ward-Leonard controlled D.C. shunt motor
(d) AC. slip ring motor
Ans: d
57. The capacity of a crane is expressed in terms of
(a) type of drive
(b) span
(c) tonnes
(d) any of the above
Ans: c
58. The characteristics of drive for crane hoisting and lowering are which of the following ?
(a) Precise control
(b) Smooth movement
(c) Fast speed control
(d) All of the above
Ans: d
59. Which of the following motors is preferred for boom hoist of a travelling crane ?
(a) Single phase motor
(b) Synchronous motor
(c) A.C. slip ring motor
(d) Ward-Leonard controlled D.C. shunt motor
Ans: c
60. A wound rotor induction motor is preferred, as compared to squirrel cage induction motor, when major consideration is
(a) slop speed operation
(b) high starting torque
(c) low windage losses
(d) all of the above
Ans: b
61. Which of the following motors has series characteristics ?
(a) Shaded pole motor
(b) Repulsion motor
(c) Capacitor start motor
(d) None of the above
Ans: b
62. Which of the following happens when star-delta starter is used ?
(a) Starting voltage is reduced
(b) Starting current is reduced
(c) Both (a) and (b)
(d) None of the above
Ans: c
63. For a D.C. shunt motor which of the following is incorrect 7
(a) Unsuitable for heavy duty starting
(b) Torque varies as armature current
(c) Torque-armature current is a straight line
(d) Torque is zero for zero armature current
Ans: a
64. For which of the following applications motor has to start with high acceleration?
(a) Oil expeller
(b) Floor mill
(c) Lifts and hoists
(d) Centrifugal pump
Ans: c
65. Which of the following types of motor enclosure is safest ?
(a) Totally enclosed
(b) Totally enclosed fan cooled
(c) Open type
(d) Semi closed
Ans: b
66. While selecting motor for an air conditioner which of the following characteristics is of great importance ?
(a) Type of bearings
(b) Type of enclosure
(c) Noise
(d) Arrangement for power transmis¬sion
(e) None of the above
Ans: c
67. The diameter of the rotor shaft for an electric motor depends on which of the following ?
(a) r.p.m. only
(b) Horse power only
(c) Horse power and r.p.m.
(d) Horse power, r.p.m. and power factor
Ans: c
68. Which of the following alternatives will be cheaper ?
(a) A 100 H.P. AC. three phase motor
(b) Four motors of 25 H.P. each
(c) Five motors of 20 H.P. each
(d) Ten motors of 10 H.P. each
Ans: a
69. The cost of an induction motor will increase as
(a) horsepower rating increases but r.p.m. decreases
(b) horsepower rating decreases but r.p.m. increases
(c) horsepower rating and operating speed increases
(d) horsepower rating and operating speed decreases
Ans: a
70. In series motor which of the following methods can be used for changing the flux per pole ?
(a) Tapped field control
(b) Diverter field control
(c) Series-parallel control
(d) Any of the above
Ans: d
Current Electricity
1. The S.I. unit of power is
(a) henry
(b) coulomb
(c) watt
(d) watt-hour
Ans: c
2. Electric pressure is also called
(a) resistance
(b) power
(c) voltage
(d) energy
Ans: c
3. The substances whfch have a large number of free electrons and offer a low resistance are called
(a) insulators
(b) inductors
(c) semi-conductors
(d) conductors
Ans: d
4. Out of the following which is not a poor conductor ?
(a) Cast iron
(b) Copper
(c) Carbon
(d) Tungsten
Ans: b
5. Out of the following which is an insulating material ?
(a) Copper
(b) Gold
(c) Silver
(d) Paper
Ans: d
6. The property of a conductor due to which it passes current is called
(a) resistance
(b) reluctance
(c) conductance
(d) inductance
Ans: c
7. Conductance is reciprocal of
(a) resistance
(b) inductance
(c) reluctance
(d) capacitance
Ans: a
8. The resistance of a conductor varies inversely as
(a) length
(6) area of cross-section
(c) temperature
(d) resistivity
Ans: b
9. With rise in temperature the resistance of pure metals
(a) increases
(b) decreases
(c) first increases and then decreases
(d) remains constant
Ans: a
10. With rise in temperature the resistance of semi-conductors
(a) decreases
(b) increases
(c) first increases and then decreases
(d) remains constant
Ans: a
11. The resistance of a copper wire 200 m long is 21 Q. If its thickness (diameter) is 0.44 mm, its specific resistance is
around
(a) 1.2 x 10~8 Q-m
(b) 1.4 x 10~8 Q-m
(c) 1.6 x 10""8 Q-m
(d) 1.8 x 10"8 Q-m
Ans: c
12. Three resistances of 10 ohms, 15 ohms and 30 ohms are connected in parallel.
The total resistance of the combination is
(a) 5 ohms
(b) 10 ohms
(c) 15 ohms
(d) 55 ohms
Ans:
13. An instrument which detects electric current is known as
(a) voltmeter
(b) rheostat
(c) wattmeter
(d) galvanometer
Ans: d
14. In a circuit a 33 Q resistor carries a current of 2 A. The voltage across the
resistor is
(a) 33 V
(b) 66 v
(c) 80 V
(d) 132 V
Ans: b
15. A light bulb draws 300 mA when the voltage across it is 240 V. The resistance of the light bulb is
(a) 400 Q
(b) 600 Q
(c) 800 Q
(d) 1000 Q
Ans: c
16. The resistance of a parallel circuit consisting of two branches is 12 ohms. If the resistance of one branch is 18 ohms, what is the resistance of the other ?
(a) 18 Q
(b) 36 Q
(c) 48 Q
(d) 64 Q
Ans: b
17. Four wires of same material, the same cross-sectional area and the same length when connected in parallel give a resistance of 0.25 Q. If the same four wires are connected is series the effective resistance will be
(a) 1 Q
(b) 2 Q
(c) 3 Q
(d) 4 Q
Ans: d
18. A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms
respectively. The current in each branch is
(a) 6.4 A, 6.9 A
(b) 6.4 A, 9.6 A
(c) 4.6 A, 6.9 A
(d) 4.6 A, 9.6 A
Ans: b
19. Current velocity through a copper conductor is
(a) the same as propagation velocity of electric energy
(b) independent of current strength
(c) of the order of a few ^.s/m
(d) nearly 3 x 108 m/s
Ans: c
20. Which of the following material has nearly zero temperature co-efficient of resistance?
(a) Manganin
(b) Porcelain
(c) Carbon
(d) Copper
Ans: a
21. You have to replace 1500 Q resistor in radio. You have no 1500 Q resistor but have several 1000 Q ones which you would connect
(a) two in parallel
(b) two in parallel and one in series
(c) three in parallel
(d) three in series
Ans: b
22. Two resistors are said to be connected in series when
(a) same current passes in turn through both
(b) both carry the same value of current
(c) total current equals the sum of branch currents
(d) sum of IR drops equals the applied e.m.f.
Ans: a
23. Which of the following statement is true both for a series and a parallel D.C. circuit?
(a) Elements have individual currents
(b) Currents are additive
(c) Voltages are additive
(d) Power are additive
Ans: d
24. Which of the following materials has a negative temperature co-efficient of resistance?
(a) Copper
(b) Aluminum
(c) Carbon
(d) Brass
Ans: c
25. Ohm's law is not applicable to
(a) vacuum tubes
(b) carbon resistors
(c) high voltage circuits
(d) circuits with low current densities
Ans: a
26. Which is the best conductor of electricity ?
(a) Iron
(b) Silver
(c) Copper
(d) Carbon
Ans: b
27. For which of the following 'ampere second' could be the unit ?
(a) Reluctance
(b) Charge
(c) Power
(d) Energy
Ans: b
28. All of the following are equivalent to watt except
(a) (amperes) ohm
(b) joules/sec.
(c) amperes x volts
(d) amperes/volt
Ans: d
29. A resistance having rating 10 ohms, 10W is likely to be a
(a) metallic resistor
(b) carbon resistor
(c) wire wound resistor
(d) variable resistor
Ans: c
30. Which one of the following does not have negative temperature co-efficient ?
(a) Aluminium
(b) Paper
(c) Rubber
(d) Mica
Ans: a
31. Varistors are
(a) insulators
(6) non-linear resistors
(c) carbon resistors
(d) resistors with zero temperature coefficient
Ans: b
32. Insulating materials have the function of
(a) preventing a short circuit between conducting wires
(b) preventing an open circuit between the voltage source and the load
(c) conducting very large currents
(d) storing very high currents
Ans: b
33. The rating of a fuse wire is always expressed in
(a) ampere-hours
(b) ampere-volts
(c) kWh
(d) amperes
Ans: d
34. The minimum charge on an ion is
(a) equal to the atomic number of the atom
(b) equal to the charge of an electron
(c) equal to the charge of the number of electrons in an atom (#) zero
Ans: b
35. In a series circuit with unequal resistances
(a) the highest resistance has the most of the current through it
(b) the lowest resistance has the highest voltage drop
(c) the lowest resistance has the highest current
(d) the highest resistance has the highest voltage drop
Ans: d
36. The filament of an electric bulb is made of
(a) carbon
(b) aluminium
(c) tungsten
(d) nickel
Ans: c
37. A 3 Q resistor having 2 A current will dissipate the power of
(a) 2 watts
(b) 4 watts
(c) 6 watts
(d) 8 watts
Ans: c
38. Which of the following statement is true?
(a) A galvanometer with low resistance in parallel is a voltmeter
(b) A galvanometer with high resis¬tance in parallel is a voltmeter
(c) A galvanometer with low resistance in series is an ammeter
(d) A galvanometer with high resis¬tance in series is an ammeter
Ans: c
39. The resistance of a few metres of wire conductor in closed electrical circuit is
(a) practically zero
(b) low
(c) high
(d) very high
Ans: a
40. If a parallel circuit is opened in the main line, the current
(a) increases in the branch of the lowest resistance
(b) increases in each branch
(c) is zero in all branches
(d) is zero in the highest resistive branch
Ans: c
41. If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes
(a) 0.4 ohm
(b) 0.6 ohm
(c) 0.8 ohm
(d) 1.0 ohm
Ans: a
42. Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open
(a) there will be heavy current in the main line
(b) rest of the two bulbs will not light
(c) all three bulbs will light
(d) the other two bulbs will light
Ans: d
43. The four bulbs of 40 W each are connected in series wifti a battery across them, which of the following statement is true ?
(a) The current through each bulb in same
(b) The voltage across each bulb is not same
(c) The power dissipation in each bulb is not same
(d) None of the above
Ans: a
44. Two resistances Rl and Ri are connected in series across the voltage source where R2>Ri. The largest drop
will be across
(a) R2
(b) Ri
(c) either Rl or Rz
(d) none of them
Ans: a
45. What will be energy used by the battery if the battery has to drive 6.28 x 1018 electrons with potential difference of 20 V across the terminal ?
(a) 5 joules
(b) 10 joules
(c) 15 joules
(d) 20 joules
Ans:
46. A closed switch has a resistance of
(a) zero
(b) about 50 ohms
(c) about 500 ohms
(d) infinity
Ans: a
47. The hot resistance of the bulb's fila¬ment is higher than its cold resistance because the temperature co-efficient of the filament is
(a) zero
(b) negative
(c) positive
(d) about 2 ohms per degree
Ans: c
48. Heat in a conductor is produced on the passage of electric current due to
(a) reactance
(b) capacitance
(c) impedance
(d) resistance
Ans:
49. The insulation on a current carrying conductor is provided
(a) to prevent leakage of current
(b) to prevent shock
(c) both of above factors
(d) none of above factors
Ans: c
50. The thickness of insulation provided on the conductor depends on
(a) the magnitude of voltage on the con-ductor
(b) the magnitude of current flowing through it
(c) both (a) and (b)
(d) none of the above
Ans: a
51. Which of the following quantities remain the same in all parts of a series circuit ?
(a) Voltage
(b) Current
(c) Power
(d) Resistance
Ans: b
52. A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the heater output will
(a) decrease
(b) increase
(c) remain same
(d) heater will burn out
Ans: b
53. In an electric kettle water boils in 10m minutes. It is required to boil the boiler in 15 minutes, using same supply mains
(a) length of heating element should be decreased
(b) length of heating element should be increased
(c) length of heating element has no effect on heating if water
(d) none of the above
Ans: a
54. An electric filament bulb can be worked from
(a) D.C. supply only
(b) A.C. supply only
(c) Battery supply only
(d) All above
Ans: d
55. Resistance of a tungsten lamp as applied voltage increases
(a) decreases
(b) increases
(c) remains same
(d) none of the above
Ans: b
56. Electric current passing through the circuit produces
(a) magnetic effect
(b) luminous effect
(c) thermal effect
(d) chemical effect
(e) all above effects
Ans: c
57. Resistance of a material always decreases if
(a) temperature of material is decreased
(6) temperature of material is increased
(c) number of free electrons available become more
(d) none of the above is correct
Ans: c
58. If the efficiency of a machine is to be high, what should be low ?
(a) Input power
(b) Losses
(c) True component of power
(d) kWh consumed
(e) Ratio of output to input
Ans: b
59. When electric current passes through a metallic conductor, its temperature rises. This is due to
(a) collisions between conduction electrons and atoms
(b) the release of conduction electrons from parent atoms
(c) mutual collisions between metal atoms
(d) mutual collisions between conducting electrons
Ans: a
60. Two bulbs of 500 W and 200 W rated at 250 V will have resistance ratio as
(a) 4 : 25
(b) 25 : 4
(c) 2 : 5
(d) 5 : 2
Ans: c
61. A glass rod when rubbed with silk cloth is charged because
(a) it takes in proton
(b) its atoms are removed
(c) it gives away electrons
(d) it gives away positive charge
Ans: c
62. Whether circuit may be AC. or D.C. one, following is most effective in reducing the magnitude of the current.
(a) Reactor
(b) Capacitor
(c) Inductor
(d) Resistor
Ans: d
63. It becomes more difficult to remove
(a) any electron from the orbit
(6) first electron from the orbit
(c) second electron from the orbit
(d) third electron from the orbit
Ans: d
64. When one leg of parallel circuit is opened out the total current will
(a) reduce
(b) increase
(c) decrease
(d) become zero
Ans: c
65. In a lamp load when more than one lamp are switched on the total resistance of the load
(a) increases
(b) decreases
(c) remains same
(d) none of the above
Ans: b
66. Two lamps 100 W and 40 W are connected in series across 230 V (alternating).
Which of the following statement is correct ?
(a) 100 W lamp will glow brighter
(b) 40 W lamp will glow brighter
(c) Both lamps will glow equally bright
(d) 40 W lamp will fuse
Ans: b
67. Resistance of 220 V, 100 W lamp will be
(a) 4.84 Q
(b) 48.4 Q
(c) 484 ft
(d) 4840 Q
Ans: c
68. In the case of direct current
(a) magnitude and direction of current remains constant
(b) magnitude and direction of current changes with time
(c) magnitude of current changes with time
(d) magnitude of current remains con¬stant
Ans: a
69. When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is
(a) A.C.
(b) D.C.
(c) any of above two
(d) none of the above
Ans: b
70. Resistance of carbon filament lamp as the applied voltage increases.
(a) increases
(b) decreases
(c) remains same
(d) none of the above
Ans: b
71. Bulbs in street lighting are all connected in
(a) parallel
(b) series
(c) series-parallel
(d) end-to-end
Ans: a
72. For testing appliances, the wattage of test lamp should be
(a) very low
(b) low
(c) high
(d) any value
Ans: c
73. Switching of a lamp in house produces noise in the radio. This is because switching operation produces
(a) arcs across separating contacts
(b) mechanical noise of high intensity
(c) both mechanical noise and arc be¬tween contacts
(d) none of the above
Ans: a
74. Sparking occurs when a load is switched off because the circuit has high
(a) resistance
(b) inductance
(c) capacitance
(d) impedance
Ans: b
75. Copper wire of certain length and resistance is drawn out to three times its length without change in volume, the new resistance of wire becomes
(a) 1/9 times
(b) 3 times
(e) 9 times
(d) unchanged
Ans: c
76. When resistance element of a heater fuses and then we reconnect it after removing a portion of it, the power of the heater will
(a) decrease
(b) increase
(c) remain constant
(d) none of the above
Ans: b
77. A field of force can exist only between
(a) two molecules
(b) two ions
(c) two atoms
(d) two metal particles
Ans: b
78. A substance whose molecules consist of dissimilar atoms is called
(a) semi-conductor
(b) super-conducto
(c) compound
(d) insulator
Ans: c
79. International ohm is defined in terms of the resistance of
(a) a column of mercury
(b) a cube of carbon
(c) a cube of copper
(d) the unit length of wire
Ans: a
80. Three identical resistors are first connected in parallel and then in series.
The resultant resistance of the first combination to the second will be
(a) 9 times
(b) 1/9 times
(c) 1/3 times
(d) 3 times
Ans: b
91. Which method can be used for absolute measurement of resistances ?
(a) Lorentz method
(b) Releigh method
(c) Ohm's law method
(d) Wheatstone bridge method
Ans: d
92. Three 6 ohm resistors are connected to form a triangle. What is the resistance between any two corners ?
(a) 3/2 Q
(b 6 Q
(c) 4 Q
(d) 8/3 Q
Ans: c
93. Ohm's law is not applicable to
(a) semi-conductors
(b) D.C. circuits
(c) small resistors
(d) high currents
Ans: a
94. Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be
(a) 160 ohms
(b) 80 ohms
(c) 20 ohms
(d) 10 ohms
Ans: d
95. A nichrome wire used as a heater coil has the resistance of 2 £2/m. For a heater of 1 kW at 200 V, the length of wire required will be
(a) 80 m
(b) 60 m
(c) 40 m
(d) 20 m
Ans: a
96. Temperature co-efficient of resistance is expressed in terms of
(a) ohms/°C
(b) mhos/ohm°C
(e) ohms/ohm°C
(d) mhos/°C
Ans: c
97. Which of the following materials has the least resistivity ?
(a) Zinc
(b) Lead
(c) Mercury
(d) Copper
Ans:
98. When current flows through heater coil it glows but supply wiring does not glow because
(a) current through supply line flows at slower speed
(b) supply wiring is covered with in¬sulation layer
(c) resistance of heater coil is more than the supply wires
(d) supply wires are made of superior material
Ans: c
99. The condition for the validity under Ohm's law is that
(a) resistance must be uniform
(b) current should be proportional to the size of the resistance
(c) resistance must be wire wound type
(d) temperature at positive end should be more than the temperature at negative end
Ans: a
100. Which of the following statement is correct ?
(a) A semi-conductor is a material whose conductivity is same as be¬tween that of a conductor and an insulator
(b) A semi-conductor is a material which has conductivity having average value of conductivity of metal and insulator
(c) A semi-conductor is one which con¬ducts only half of the applied voltage
(d) A semi-conductor is a material made of alternate layers of conducting material and insulator
Ans: a
101. A rheostat differs from potentiometer in the respect that it
(a) has lower wantage rating
(b) has higher wattage rating
(c) has large number of turns
(d) offers large number of tappings
Ans: b
102. The weight of an aluminium conductor as compared to a copper conductor of identical cross-section, for the same electrical resistance, is
(a) 50%
(b) 60%
(c) 100%
(d) 150%
Ans: a
103. An open resistor, when checked with an ohm-meter reads
(a) zero
(b) infinite
(c) high but within tolerance
(d) low but not zero
Ans: b
104. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.
(a) Varistors
(b) Thermistor
(c) Semi-conductors
(d) Variable resistors
Ans: c
105. All good conductors have high
(a) conductance
(b) resistance
(c) reluctance
(d) thermal conductivity
Ans: a
106. Voltage dependent resistors are usually made from
(a) charcoal
(b) silicon carbide
(c) nichrome
(d) graphite
Ans: c
107. Voltage dependent resistors are used
(a) for inductive circuits
(6) to supress surges
(c) as heating elements
(d) as current stabilizers
Ans: b
108. The ratio of mass of proton to that of electron is nearly
(a) 1840
(b) 1840
(c) 30
(d) 4
Ans: a
109. The number of electrons in the outer most orbit of carbon atom is
(a) 3
(b) 4
(c) 6
(d) 7
Ans: b
110. With three resistances connected in parallel, if each dissipates 20 W the total power supplied by the voltage source equals
(a) 10 W
(b) 20 W
(c) 40 W
(d) 60 W
Ans: d
111. A thermistor has
(a) positive temperature coefficient
(b) negative temperature coefficient
(c) zero temperature coefficient
(d) variable temperature coefficient
Ans: c
112. If/, R and t are the current, resistance and time respectively, then according to Joule's law heat produced will be proportional to
(a) I2Rt
(b) I2Rf
(c) I2R2t
(d) I2R2t*
Ans: a
113. Nichrome wire is an alloy of
(a) lead and zinc
(b) chromium and vanadium
(c) nickel and chromium
(d) copper and silver
Ans: c
114. When a voltage of one volt is applied, a circuit allows one microampere current to flow through it. The conductance of the circuit is
(a) 1 n-mho
(b) 106 mho
(c) 1 milli-mho
(d) none of the above
Ans: a
115. Which of the following can have negative temperature coefficient ?
(a) Compounds of silver
(6) Liquid metals
(c) Metallic alloys
(d) Electrolytes
Ans: d
116. Conductance : mho ::
(a) resistance : ohm
(b) capacitance : henry
(c) inductance : farad
(d) lumen : steradian
Ans: a
117. 1 angstrom is equal to
(a) 10-8 mm
(6) 10"6 cm
(c) 10"10 m
(d) 10~14 m
Ans: c
118. One newton metre is same as
(a) one watt
(b) one joule
(c) five joules
(d) one joule second
Ans: b
Dc Generator
1. Laminations of core are generally made of
(a) case iron
(b) carbon
(c) silicon steel
(d) stainless steel
Ans: c
2. Which of the following could be lamina-proximately the thickness of lamina-tions of a D.C. machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m
(d) 5 m
Ans: c
3. The armature of D.C. generator is laminated to
(a) reduce the bulk
(b) provide the bulk
(c) insulate the core
(d) reduce eddy current loss
Ans: d
4. The resistance of armature winding depends on
(a) length of conductor
(b) cross-sectional area of the conductor
(c) number of conductors
(d) all of the above
Ans: d
5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: b
6. The commutator segments are connected to the armature conductors by means of
(a) copper lugs
(b) resistance wires
(c) insulation pads
(d) brazing
Ans: a
7. In a commutator
(a) copper is harder than mica
(b) mica and copper are equally hard
(c) mica is harder than copper
(d) none of the above
Ans: c
8. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets
(b) counter sunk screws
(c) brazing
(d) welding
Ans: b
9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor
(b) lines of force
(c) either of the above
(d) none of the above
Ans: b
10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force
(b) magnetic flux, direction of motion and the direction of e.m.f. induced
(c) magnetic field strength, induced voltage and current
(d) magnetic flux, direction of force and direction of motion of conductor
Ans: b
11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(d) direction of motion of conductor, if forefinger points along the lines of flux
Ans: d
12. The bearings used to support the rotor shafts are generally
(a) ball bearings
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings
Ans: a
13. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above
Ans: d
14. In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles
(c) half the number of poles
(d) two
Ans: b
15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
(a) Lap winding
(b) Wave winding
(c) Either of (a) and (b) above
(d) Depends on other features of design
Ans: b
16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south
(c) all the four poles are south poles
(d) two north poles follow two south poles
Ans: b
17. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved
(b) where high voltage and small cur-rents are involved
(c) in both of the above cases
(d) in none of the above cases
Ans: a
18. A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage con-trol
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features
Ans: d
19. In case of D.C. machines, mechanical losses are primary function of
(a) current
(b) voltage
(c) speed
(d) none of above
Ans: c
20. Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load
(c) voltage
(d) speed and voltage
Ans: b
21. In D.C. generators, current to the external circuit from armature is given through
(a) commutator
(b) solid connection
(c) slip rings
(d) none of above
Ans: a
23. Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper
(d) all of above
Ans: a
24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Blv
(b)Blv2
(c)Bl2v
(d)Bl2v2
Ans: a
25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32
Ans: b
26. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: d
27. The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish
Ans: c
28. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a) lie under south pole
(b) lie under north pole
(c) lie under interpolar region
(d) are farthest from the poles
Ans: c
29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
(a) demagnetisation only
(b) cross magnetisation as well as magnetisation
(c) crossmagnetisation as well as demagnetising
(d) cross magnetisation only
Ans: c
30. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising
(d) none of above
Ans: a
31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above
Ans: d
32. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature
(d) all above
Ans: c
33. In a D.C. machine, short-circuited field coil will result in
(a) odour of barning insulation
(b) unbalanced magnetic pull producing vibrations
(c) reduction of generated voltage for which excitation has to be increased to maintain the voltage
(d) all above
Ans:
34. Equilizer rings are required in case armature is
(a) wave wound
(b) lap wound
(c) delta wound
(d) duplex wound
Ans: b
35. Welding generator will have
(a) lap winding
(b) wave winding
(c) delta winding
(d) duplex wave winding
Ans: a
36. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns
Ans: a
37. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a) rotary converter
(b) mercury are rectifier
(c) induction motor D.C. generator set
(d) synchronous motor D.C. generator set
Ans: c
38. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the magnetic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions
Ans: d
39. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches
Ans: d
40. A D.C. welding generator has
(a) lap winding
(b) wave moving
(c) duplex winding
(d) any of the above
Ans: a
41. Which of the following statement about D.C. generators is false ?
(a) Compensating winding in a D.C. machine helps in commutation
(b) In a D. C. generator interpoles winding is connected in series with the armature winding
(c) Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d) Equilizing bus bars are used with parallel running of D.C. shunt generators
Ans: d
42. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble
Ans: a
43. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above
Ans: a
44. The number of brushes in a commutator depends on
(a) speed of armature
(b) type of winding
(c) voltage
(d) amount of current to be collected
Ans: d
45. Compensating windings are used in D.C. generators
(a) mainly to reduce the eddy currents by providing local short-circuits
(b) to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction
(d) none of the above
Ans: c
46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
(a) Dummy coils
(b) Commutator
(c) Eye bolt
(d) Equilizer rings
Ans: b
47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a) using conductor of annealed copper
(b) using commutator with large number of segments
(c) using carbon brushes of superior quality
(d) using equiliser rings
Ans: c
48. In D.C. generators, lap winding is used for
(a) high voltage, high current
(b) low voltage, high current
(c) high voltage, low current
(d) low voltage, low current
Ans: b
49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3
(b) 3 : 1
(c) 3 : 2
(d) 1 : 3
Ans: b
50. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes
(d) None of the above
Ans: c
51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be
(a) E/2
(b) 2E
(c) slightly less than E
(d) E
Ans: b
52. In a D.C. generator the actual flux distribution depends upon
(a) size of air gap
(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent pole shoes
(d) all of the above
Ans:
53. The armature core of a D.C. generator is usually made of
(a) silicon steel
(b) copper
(c) non-ferrous material
(d) cast-iron
Ans: a
9.63. Satisfactory commutation of D.C. machines requires
(a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders
(c) smooth, concentric commutator properly undercut
(d) all of the above
Ans: d
54. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is connected
(b) indicated by a spark completely around the commutator
(c) both (a) and (b)
(d) none of the above
Ans: c
55. In a D.C. machine, fractional pitch winding is used
(a) to increase the generated voltage
(b) to reduce sparking
(c) to save the copper because of shorter end connections
(d) due to (b) and (c) above
Ans:
56. For the parallel operation of two or more D.C. compound generators, we should ensure that
(a) voltage of the incoming generator should be same as that of bus bar
(b) polarity of incoming generator should be same as that of bus bar
(c) all the series fields should be run in parallel by means of equilizer connection
(d) series fields of all generators should be either on positive side or negative side of the armature
(e) all conditions mentioned above should be satisfied
Ans: d
57. D.C. series generator is used
(a) to supply traction load
(b) to supply industrial load at constant voltage
(c) voltage at the toad end of the feeder
(d) for none of the above purpose
Ans: c
58. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
(a) series generator
(b) shunt generator
(c) compound generator
(d) self-excited generator
Ans: d
59. Interpole flux should be sufficient to
(a) neutralise the commutating self induced e.m.f.
(b) neutralise the armature reaction flux
(c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
(d) perform none of the above functions
Ans: c
60. D.C. generator generally preferred for charging automobile batteries is
(a) series generator
(b) shunt generator
(c) long shunt compound generator
(d) any of'the above
Ans: c
61. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
(a) r.p.m. is more than 300
(b) r.p.m. is less than 300
(c) number of poles is 4
(d) number of poles is 2
Ans: d
62. Permeance is the reciprocal of
(a) flux density
(b) reluctance
(c) ampere-turns
(d) resistance
Ans: b
63. In D.C. generators the polarity of the interpoles
(a) is the same as that of the main pole ahead
(b) is the same as that of the immediately preceding pole
(c) is opposite to that of the main pole ahead
(d) is neutral as these poles do not play part in generating e.m.f.
Ans: a
64. The e.m.f. generated in a D.C. generator is directly proportional to
(a) flux/pole
(b) speed of armature
(c) number of poles
(d) all of the above
Ans: b
65. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when
(a) there is no load on|he generator
(b) the generator runs on full load
(c) the generator runs on overload
(d) the generator runs on designed speed
Ans: a
66. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except
(a) interpoles
(b) dummy coils
(c) compensating winding
(d) shifting of axis of brushes
Ans: b
67. In D.C. generators on no-load, the air gap flux distribution in space is
(a) sinusoidal
(b) triangular
(c) pulsating
(d) flat topped
Ans: d
68. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly
(a) 150 V
(b) 175 V
(c) 240 V
(d) 290 V
Ans: c
69. The purpose of providing dummy coils in a generator is
(a) to reduce eddy current losses
(b) to enhance flux density
(c) to amplify voltage
(d) to provide mechanical balance for the rotor
Ans: d
70. In a shunt generator the voltage build up is generally restricted by
(a) speed limitation
(b) armature heating
(c) insulation restrictions
(d) saturation of iron
Ans:
71. If a D.C. generator fails to build up the probable cause could not be
(a) imperfect brush contact
(b) field resistance less than the critical resistance
(c) no residual magnetism in the generator
(d) faulty shunt connections tending to reduce the residual magnetism
Ans: b
72. Flashing the field of D.C. generator means
(a) neutralising residual magnetism
(b) creating residual magnetism by a D.C. source
(c) making the magnetic losses of forces parallel
(d) increasing flux density by adding extra turns of windings on poles
Ans: b
73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
(a) 640 V
(b) 620 V
(c) 600 V
(d) 580 V
Ans: d
74. In a D.C. generator the critical resistance refers to the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b
75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis
Ans: a
76. Armature coil is short circuited by brushes when it lies
(a) along neutral axis
(b) along field axis
(c) in any of the above positions
(d) in none of the above positions
Ans: a
77. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt
(c) cumulatively compounded short shunt
(d) differentially compounded short shunt
Ans: b
78. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other
(b) the brushes of same polarity should track each other
(c) brush position has no effect on the commutator grooving
Ans: a
79. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two com-mutator bars
(6) Insulation failure between two turns of a coil
(c) Two of more turns of the same coil getting grounded
(d) All of the above
Ans: d
80. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) high mica insulation between com-mutation bars
(e) all of the above factors
Ans: e
81. Number of tappings for each equilizer ring is equal to
(a) number of pole pairs
(b) number of poles
(c) number of parallel paths
(d) number of commutator segments
Ans: a
82. A D.C. generator can be considered as
(a) rectifier
(b) primemover
(c) rotating amplifier
(d) power pump
Ans: c
83. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called
(a) rotor
(b) stator
(c) field
(d) armature
Ans: d
84. In a D.C. machine stray loss is the sum of
(a) total copper loss and mechanical loss
(b) armature copper loss and iron loss
(c) shunt field copper loss and mechanical loss
(d) iron loss and mechanical loss
Ans: d
85. Lap winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles
Ans: a
86. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
(a) increase
(b) decrease
(c) remain unaffected
(d) fluctuate heavily
Ans: b
87. An exciter for a turbo generator is a
(a) separately excited generator
(b) shunt generator
(c) series generator
(d) compound generator
Ans: b
88. In case of a flat compounded generator
(a) voltage generated is less than the rated voltage
(b) generated voltage is proportional to the load on the generator
(c) voltage remains constant irrespec¬tive of the load
(d) speed varies in proportion to the load on the generator
Ans: c
89. Which of the following generator will have negligible terminal voltage while running on no-load ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) Separately excited generator
Ans: a
90. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) None of the above
Ans: d
91. In over compounded generator, full load terminal voltage is
(a) almost zero
(b) less than noload terminal voltage
(c) more than noload terminal voltage
(d) equal to no-load terminal voltage
Ans: c
92. In a level compounded D.C. generator, full load terminal voltage is
(a) negligibly low
(b) equal to no-load terminal voltage
(c) more than no-load terminal voltage
(d) less than no-load terminal voltage
Ans: b
93. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(a) armature reaction
(b) armature resistance drop
(c) field weakening due to armature reaction and armature
(d) commutation
Ans: d
94. In a D.C. generator
(a) external resistance = internal char-acteristic - armature reaction
(b) internal characteristic = magnetisation characteristic - ohmic drop
(c) external characteristic = magnetisation characteristic - ohmic drop - armature reaction
(d) magnetisation characteristic = external characteristic
Ans: c
95. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
(a) will be zero
(b) will be of 5 Hz
(c) willbeof5xiVHz
(d) will be of v Hz 5
Ans: b
96. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(a) zero
(b) about 2 V
(c) about 50 V
(d) 220 V
Ans: b
97. In a separately excited generator supplying rated load the armature reaction ,
(a) is always present
(b) is always absent
(c) may be sometimes present
(d) none of the above
Ans: a
98. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(a) zero
(b) small
(c) the same as rated voltage
(d) high
Ans: a
99. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip
(b) demagnetisation of trailing pole tip and magnetisation of leading pole tip
(c) damagnetising the centre of all poles
(d) magnetising the centre of all poles
Ans: a
100. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Series field
(b) Compensating field
(c) Inter pole field
(d) Shunt field
Ans: d
101. Wave winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles
Ans: c
102. The critical resistance of the D.C. generator is the resistance of
(a) field
(b) brushes
(c) armature
(d) load
Ans: a
103. When two D.C. series generators are running in parallel, an equilizer bar is used
(a) to increase the speed and hence generated e.m.f.
(b) to increase the series flux
(c) so that two similar machines will pass approximately equal currents to the load
(d) to reduce the combined effect of ar-mature reaction of both machines
Ans: c
104. Which of the following generating machine will offer constant voltage on all loads ?
(a) Self-excited generator
(b) Separately excited generator
(c) Level compounded generator .
(d) All of the above
Ans: c
105. Which of the following generators will be preferred if they are required to be run in parallel ?
(a) Shunt generators
(b) Series generators
(c) Compound generators
(d) None of the above
Ans: a
106. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
(a) The direction of that generator is reversed
(b) The speed of that generator is increased
(c) The field of that generator is weakened
(d) That generator takes large share of loads
Ans: d
107. A D.C. generator works on the principle of
(a) Lenz's law
(b) Ohm's law
(c) Faraday's law of electromagnetic induction
(d) none of the above
Ans: c
108. A series generator can self-excite
(a) only if the load current is zero
(b) only if the load current is not zero
(c) irrespective of the value of load current
(d) none of the above
Ans: b
109. A shunt generator can self-excite
(a) only if the resistance of the field circuit is less than critical value
(b) only if the resistance of the field circuit is greater than critical value
(c) irrespective of the value of the resis-tance in the field circuit
Ans: a
110. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
(a) 150 V
(b) less than 150 V
(c) greater than 150 V
(d) none of the above
Ans: c
111. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(a) will be less than 250 V
(b) will always be 250 V
(c) may be greater or less than 250 V
(d) none of the above
Ans: c
112. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
(a) 270 V
(b) 267.5 V
(c) 265 V
(d) 257.4 V
Ans: b
113. The essential condition for parallel operation of two D.C. generators is that they have '
(a) same kW rating
(b) the same operation r.p.m.
(c) the same drooping voltage charac-teristics
(d) same percentage regulation
Ans: c
114. When two D.C. generators are running in parallel an equilizer bar is used
(a) to increase the series flux
(b) to increase the generated e.m.f.
(c) to reduce the combined effect of ar-mature reaction of both the machines
(d) so that the two identical machines will pass approximately equal currents to the load
Ans: d
115. With a D.C. generator which of the following regulation is preferred ?
(a) 100% regulation
(b) infinite regulation
(c) 50% regulation
(d) 1% regulation
Ans: d
116. Which generator would you prefer for feeding long D.C. transmission lines ?
(a) Series generator
(b) Shunt generator
(c) Over compound generator
(d) Flat compound generator
Ans: c
117. In a D.C. generator the critical resistance can be increased by
(a) increasing its field resistance
(b) decreasing its field resistance
(c) increasing its speed
(d) decreasing its speed
Ans: c
118. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b
119. For both lap and wave windings, there are as many commutator bars as the number of
(a) slots
(b) armature conductors
(c) winding elements
(d) poles
Ans: c
120. The series field of a short-shunt D.C. generator is excited by
(a) external current
(b) armature current
(c) shunt current
(d) load current
Ans: d
121. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately
(a) 40 percent
(b) 25 percent
(c) 10 percent
(d) 5 percent
Ans: d
122. Shunt generators are most suited for stable parallel operation because of their
(a) rising voltage characteristics
(b) identical voltage characteristics
(c) drooping voltage characteristics
(d) linear voltage characteristics
Ans: c
123. The main factor which leads to unstable parallel operation of flat and over compounded generators is
(a) their rising voltage characteristics
(b) unequal number of turns in their series field windings
(c) unequal speed regulation of their primemovers
(d) unequal series field resistances
Ans: a
124. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to
(a) reverse the field connections
(b) increase the field resistance
(c) increase the speed of primemover
(d) check armature insulation resis¬tance
Ans: a
Dc Motors
1. No-load speed of which of the following motor will be highest ?
(a) Shunt motor
(b) Series motor
(c) Cumulative compound motor
(d) Differentiate compound motor
Ans: b
2. The direction of rotation of a D.C. series motor can be changed by
(a) interchanging supply terminals
(b) interchanging field terminals
(c) either of (a) and (b) above
(d) None of the above
Ans: b
3. Which of the following application requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower
Ans: c
4. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
(a) Series motor
(b) Shunt motor
(c) Differentially compound motor
(d) Cumulative compound motor
Ans: a
5. Which D.C. motor will be preferred for machine tools ?
(a) Series motor
(b) Shunt motor
(c) Cumulative compound motor
(d) Differential compound motor
Ans: b
6. Differentially compound D.C. motors can find applications requiring
(a) high starting torque
(b) low starting torque
(c) variable speed
(d) frequent on-off cycles
Ans: b
7. Which D.C. motor is preferred for elevators ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
(d) Cumulative compound motor
Ans: d
8. According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
(a) current in the conductor aovtaat of conductor
(c) resultant force on conductor
(d) none of the above
Ans: a
9. If the field of a D.C. shunt motor gets opened while motor is running
(a) the speed of motor will be reduced %
(b) the armature current will reduce
(c) the motor will attain dangerously high speed 1
(d) the motor will continue to nuvat constant speed
Ans: c
10. Starters are used with D.C. motors because
(a) these motors have high starting torque
(b) these motors are not self-starting
(c) back e.m.f. of these motors is zero initially
(d) to restrict armature current as there is no back e.m.f. while starting
Ans: d
11. In D.C. shunt motors as load is reduced
(a) the speed will increase abruptly
(b) the speed will increase in proportion to reduction in load
(c) the speed will remain almost/constant
(d) the speed will reduce
Ans: c
12. A D.C. series motor is that which
(a) has its field winding consisting of thick wire and less turns
(b) has a poor torque
(c) can be started easily without load
(d) has almost constant speed
Ans: a
13. For starting a D.C. motor a starter is required because
(a) it limits the speed of the motor
(b) it limits the starting current to a safe value
(c) it starts the motor
(d) none of the above
Ans: b
14. The type of D.C. motor used for shears and punches is
(a) shunt motor
(b) series motor
(c) differential compoutid D.C. motor
(d) cumulative compound D.C. motor
Ans: d
15. If a D.C. motor is connected across the A.C. supply it will
(a) run at normal speed
(b) not run
(c) run at lower speed
(d) burn due to heat produced in the field winding by .eddy currents
Ans: d
16. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
(a) Ward Leonard control
(b) rheostatic control
(c) any of the above method
(d) none of the above method
Ans: a
17. When two D.C. series motors are connected in parallel, the resultant speed is
(a) more than the normal speed
(b) loss than the normal speed
(c) normal speed
(d) zero
Ans: c
18. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a) decreasing the field current
(b) increasing the field current
(c) decreasing the armature current
(d) increasing the armature current
Ans: a
19. In a D.C. shunt motor, speed is
(a) independent of armature current
(b) directly proportional to the armature current
(c) proportional to the square of the current
(d) inversely proportional to the armature current
Ans: a
20. A direct on line starter is used: for starting motors
(a) iip to 5 H.P.
(b) up to 10 H.P.
(c) up to 15 H.P.
(d) up to 20 H.P.
Ans: a
21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a) The motor will stop
(b) The motor will continue to run
(c) The armature may burn
(d) The motor will run noisy
Ans: c
22. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a) back e.m.f. is equal to armature drop
(b) armature drop is negligible
(c) flux is proportional to armature current
(d) flux is practically constant in D:C. shunt motors
Ans: d
23. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(a) almost negligible
(b) rated full-load current
(c) less than full-load current
(d) more than full-load current
Ans: d
24. These days D.C. motors are widely used in
(a) pumping sets
(b) air compressors
(c) electric traction
(d) machine shops
Ans: c
25. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(a) Frame
(b) Shaft
(c) Commutator
(d) Stator
Ans: c
26. In which of the following applications D.C. series motor is invariably tried?
(a) Starter for a car
(b) Drive for a water pump
(c) Fan motor
(d) Motor operation in A.C. or D.C.
Ans: a
27. In D.C. machines fractional pitch winding is used
(a) to improve cooling
(b) to reduce copper losses
(c) to increase the generated e.m.f.
(d) to reduce the sparking
Ans: d
28. A three point starter is considered suitable for
(a) shunt motors
(b) shunt as well as compound motors
(c) shunt, compound and series motors
(d) all D.C. motors
Ans: b
29. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a) 100%
(b) around 90%
(c) anywhere between 75% and 90%
(d) less than 50%
Ans: d
30. The ratio of starting torque to full-load torque is least in case of
(a) series motors
(b) shunt motors
(c) compound motors
(d) none of the above
Ans: b
32. In D.C. motor which of the following can sustain the maximum temperature rise?
(a) Slip rings
(b) Commutator
(c) Field winding
(d) Armature winding
Ans: c
33. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
(a) Lenz's law
(b) Faraday's law
(c) Coloumb's law
(d) Fleming's left-hand rule
Ans: d
34. Which of the following load normally needs starting torque more than the rated torque?
(a) Blowers
(b) Conveyors
(c) Air compressors
(d) Centrifugal pumps
Ans: b
35. The starting resistance of a D.C. motor is generally
(a) low
(b) around 500 Q
(c) 1000 Q
(d) infinitely large
Ans: a
36. The speed of a D.C. series motor is
(a) proportional to the armature current
(b) proportional to the square of the armature current
(c) proportional to field current
(d) inversely proportional to the armature current
Ans: d
37. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal
to
(a) 100% of the previous value
(b) 50% of the previous value
(c) 25% of the previous value
(d) 10% of the previous value
(e) none of the above
Ans: c
38. The current drawn by the armature of D.C. motor is directly proportional to
(a) the torque required
(b) the speed of the motor
(c) the voltage across the terminals
(d) none of the above
Ans: a
39. The power mentioned on the name plate of an electric motor indicates
(a) the power drawn in kW
(b) the power drawn in kVA
(c) the gross power
(d) the output power available at the shaft
Ans: d
40. Which D.C. motor has got maximum self loading property?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded 'motor
(d) Differentially compounded motor
Ans: d
41. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: c
42. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
(a) nothing will happen to th£ motor
(b) this will make armature to take heavy current, possibly burning it
(c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses (d) motor will run at very slow speed
Ans: c
43. D.C. series motors are used
(a) where load is constant
(b) where load changes frequently
(c) where constant operating speed is needed
(d) in none of the above situations.
Ans: d
44. For the same H.P. rating and full load speed, following motor has poor starting torque
(a) shunt
(b) series
(c) differentially compounded
(d) cumulativelyc'ompounded
Ans: c
45. In case of conductively compensated D.C. series motors, the compensating winding is provided
(a) as separately wound unit
(6) in parallel with armature winding
(c) in series with armature winding
(d) in parallel with field winding
Ans: c
46. Sparking at the commutator of a D.C. motor may result in
(a) damage to commutator segments
(b) damage to commutator insulation
(c) increased power consumption
(d) all of the above
Ans: d
47. Which of the following motor is preferred for operation in highly explosive atmosphere ?
(a) Series motor
(b) Shunt motor
(c) Air motor
(d) Battery operated motor
Ans: c
48. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
(a) Starting torque
(b) Operating speed
(c) Full-load current
(d) All of the above
Ans: c
49. Which one of the following is not the function of pole shoes in a D.C. machine ?
(a) To reduce eddy current loss
(b) To support the field coils
(c) To spread out flux for better unifor-mity
(d) To reduce the reluctance of the mag-netic path
Ans: a
50. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
(a) 4.0
(b) 2.0
(c) 1.0
(d) 0.5
Ans: d
51. The condition for maximum power in case of D.C. motor is
(a) back e.m.f. = 2 x supply voltage
(b) back e.m.f. = | x supply voltage
(c) supply voltage = | x back e.m.f.
(d) supply voltage = back e.m.f.
Ans: b
52. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
(a) Low speed operation
(b) High speed operation
(c) Variable speed operation
(d) Fixed speed operation
Ans: c
53. In D.C. machines the residual magnetism is of the order of
(a) 2 to 3 per cent
(6) 10 to 15 per cent
(c) 20 to 25 per cent
(d) 50 to 75 per cent
Ans: a
54. Which D.C. motor is generally preferred for cranes and hoists ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a
55. Three point starter can be used for
(a) series motor only
(b) shunt motor only
(c) compound motor only
(d) both shunt and compound motor
Ans: d
56. Sparking, is discouraged in a D.C. motor because
(a) it increases the input power con-sumption
(b) commutator gets damaged
(c) both (a) and (b)
(d) none of the above
Ans: b
57. Speed control by Ward Leonard method gives uniform speed variation
(a) in one direction
(b) in both directions
(c) below normal speed only
(d) above normal speed only.
Ans: b
58. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have
to be
(a) level compounded
(b) under compounded
(c) cumulatively compounded
(d) differentially compounded
Ans: c
59. Following motor is used where high starting torque and wide speed range control is required.
(a) Single phase capacitor start
(b) Induction motor
(c) Synchronous motor
(d) D.C. motor
(e) None of the above
Ans: d
60. In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor
(b) the motor will work as series motor and run at slow speed in the same direction
(c) the motor will work as series motor and run at high speed in the same direction
(d) the motor will not work and come to stop
Ans: a
61. Which of the following motor has the poorest speed regulation ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
(d) Cumulative compound motor
Ans: b
62. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
(a) D.C. series motor
(b) D.C. shunt motor
(c) induction motor
(d) all of above motors
Ans: a
63. As -the load is increased the speed of D.C. shunt motor will
(a) reduce slightly
(b) increase slightly
(c) increase proportionately
(d) remains unchanged
Ans: a
64. The armature torque of the D.C. shunt motor is proportional to
(a) field flux only
(b) armature current only
(c) both (a) and (b)
(d) none of the above
Ans: b
65. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
(a) Voltage control method
(b) Field control method
(c) Armature control method
(d) All above methods
Ans: c
66. Usually wide and sensitive speed control is desired in case of
(a) centrifugal pumps
(b) elevators
(c) steel rolling mills
(d) colliery winders
Ans: d
67. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
(a) 2.36%
(6) 4.76%
(c) 6.77%
(d) 8.84%
Ans: b
68. The armature voltage control of D.C. motor provides
(a) constant torque drive
(b) constant voltage drive
(c) constant current drive
(d) none of the above
Ans: a
69. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit
(a) a resistance is connected in series with armature
(b) a resistance is connected parallel to the armature
(c) armature is temporarily open circuited
(d) a high value resistor is connected across the field winding
Ans: a
70. The speed of a D.C. shunt motor can be increased by
(a) increasing the resistance in armature circuit
(b) increasing the resistance in field circuit
(c) reducing the resistance in the field circuit
(d) reducing the resistance in the armature circuit
Ans: b
71. If I2 be the armature current, then speed of a D.C. shunt motor is
(a) independent of Ia
(b) proportional to la
(c) varies as (Ia)
(d) varies as la
Ans: a
72. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
(a) remain unchanged
(6) reduce to one-fourth value
(c) increase four folds
(d) be doubled
Ans: a
73. At the instant of starting when a D.C. motor is put on supply, it behaves like
(a) a highly resistive circuit
(6) a low resistance circuit
(c) a capacitive circuit
(d) none of the above
Ans: b
74. The speed of a D.C. motor can be varied by varying
(a) field current
(b) applied voltage
(c) resistance in series with armature
(d) any of the above
Ans: d
75. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
(a) Low cost
(b) Wide speed range
(c) Stability
(d) High starting torque.
Ans: a
76. For a D.C. shunt motor if the excitation is changed
(a) torque will remain constant
(b) torque will change but power will remain constant
(c) torque and power both will change
(d) torque, power and speed, all will change
Ans: b
77. Which motor has the poorest speed control?
(a) Differentially compounded motor
(b) Cumulatively compounded motor
(c) Shunt motor
(d) Series motor
Ans: d
78. The plugging gives the
(a) zero torque braking
(b) smallest torque braking
(c) highest torque braking
(d) none of the above
Ans: c
79. The armature voltage control of D.C. motor provides
(a) constant voltage drive
(b) constant current drive
(c) constant torque drive
(d) none of the above
Ans: c
80. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor
(a) of lower H.P. should be selected
(6) of higher H.P. should be selected
(c) can be used for 50°C ambient temperature also
(d) is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor
Ans: d
81. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
(o) regenerative
(b) plugging
(c) dynamic braking
(d) none of the above
(e) any of the above
Ans: b
82. Which of the following motors one will choose to drive the rotary compressor ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Universal motor
(d) Synchronous motor
Ans: d
83. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(a) increase
(b) decrease
(c) remain same
(d) become zero
Ans: a
84. Why are the D.C. motors preferred for traction applications ?
(a) Torque and speed are inversely proportional to armature current
(b) Torque is proportional to armature current
(c) Torque is proportional to square root of armature current
(d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current
Ans: d
85. Which of the following motors is usually used in house-hold refrigerators ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Single phase induction motor (split phase start or induction run motor)
(d) Reluctance motor
(e) Synchronous motor
Ans: c
86. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Induction motor
(d) Reluctance motor
Ans: d
87. Which motor should not be started on no-load ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor.
Ans: a
88. Ward-Leonard control is basically a
(a) voltage control method
(b) field divertor method
(c) field control method
(d) armature resistance control method
Ans: a
89. For constant torque drive which speed control method is preferred ?
(a) Field control
(b) Armature voltage control
(c) Shunt armature control
(d) Mechanical loading system
Ans: b
90. In Ward-Leonard control the lower limit of speed is imposed by
(a) residual magnetism of the generator
(b) core losses of motor
(c) mechanical losses of motor and gen¬erator together
(d) all of the above
Ans: a
91. The main disadvantage of the Ward-Leonard control method is
(a) high initial cost
(b) high maintenance cost
(c) low efficiency at Hght loads
(d) all of the above
Ans: d
92. Regenerative method of braking is based on that
(a) back e.m.f. is less than the applied voltage
(b) back e.m.f. is equal to the applied voltage
(c) back e.m.f. of rotor is more than the applied voltage
(d) none of the above
Ans: b
93. The hysteresis loss in a D.C. machine least depends on
(a) Frequency of magnetic reversals
(b) Maximum value of flux density
(c) Volume and grade of iron
(d) Rate of flow of ventilating air
Ans: d
94. In a D.C. generator all of the following could be the effects of iron losses except
(a) Loss of efficiency
(b) Excessive heating of core
(c) Increase in terminal voltage
(d) Rise in temperature of ventilating air
Ans: c
95. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
(a) hysteresis loss
(b) field copper loss
(c) armature copper loss
(d) eddy current loss
Ans: c
96. Which of the following loss in a D.C. generator varies significantly with the load current ?
(a) Field copper loss
(b) Windage loss
(c) Armature copper loss
(d) None of the above
Ans: c
97. Torque developed by a D.C. motor depends upon
(a) magnetic field
(b) active length of the conductor
(c) current flow through the conductors
(d) number of conductors
(e) radius of armature
(f) all above factors
Ans: f
98. D.C. shunt motors are used for driving
(a) trains
(b) cranes
(c) hoists
(d) machine tools
Ans: d
99. In a manual shunt motor starter
(a) over load relay is connected in series and no volt relay in parallel with the load
(6) over load relay is connected in paral¬lel and no volt relay in series with the load
(c) over load relay and no volt relay are both connected in series with the load
(d) over load relay and no volt relay are both connected in parallel with the load
Ans: a
100. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
(a) Providing laminations in armature core
(b) Providing laminations in stator
(c) Using non-magnetic material for frame
(d) Using material of low hysteresis co-efficient for armature core material
Ans: d
101. Which of the following loss in a D.C. generator is dissipated in the form of heat?
(a) Mechanical loss
(b) Core loss
(c) Copper loss
(d) All of the above
Ans: d
102. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
(a) Hysteresis losses
(b) Eddy current losses
(c) Copper losses
(d) Windage losses
Ans: b
103. The total losses in a well designed D.C. generator of 10 kW will be nearly
(a) 100 W
(b) 500 W
(c) 1000 W
(d) 1500 W
Ans: b
104. The condition for maximum efficiency for a D.C. generator is
(a) eddy current losses = stray losses
(b) hysteresis losses = eddy current losses
(c) copper losses = 0
(d) variable losses = constant losses
Ans: d
105. D.C. generators are normally designed for maximum efficiency around
(a) full-load
(b) rated r.p.m.
(c) rated voltage
(d) all of the above
Ans: a
106. In a D.C. generator, the iron losses mainly take place in
(a) yoke
(b) commutator
(c) armature conductors
(d) armature rotor
Ans: d
107. D.C. generators are installed near the load centres to reduce
(a) iron losses
(b) line losses
(c) sparking
(d) corona losses
Ans: b
108. The purpose of retardation test on D.C. shunt machines is to find out
(a) stray losses
(b) eddy current losses
(c) field copper losses
(d) windage losses
Ans: a
109. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
(a) Swinburne's test
(b) Hopkinson's test
(c) Field test
(d) Brake test
Ans: c
110. Hopkinson's test on D.C. machines is conducted at
(a) no-load
(b) part load
(c) full-load
(d) overload
Ans: c
111. During rheostat braking of D.C. series motors
(a) motor is run as a generator
(b) motor is reversed in direction
(c) motor is run at reduced speed
Ans: a
112. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors
(b) Series motors
(c) Compound motors
(d) All of the above
Ans: d
113. Which method of braking is generally used in elevators ?
(a) Plugging
(b) Regenerative braking
(c) Rheostatic braking
(d) None of the above
Ans: a
114. In variable speed motor
(a) a stronger commutating field is needed at low speed than at high speed
(b) a weaker commutating field is needed at low speed than at high speed
(c) same commutating field is needed at low speed than at high speed
(d) none of the above is correct
Ans: b
115. When the armature of a D.C. motor rotates, e.m.f. induced is
(a) self-induced e.m.f.
(b) mutually induced e.m.f.
(c) back e.m.f.
(d) none of the above
Ans: c
116. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
(a) drum type controller is used
(b) three point starter is used
(c) four point starter is used
(d) all above can be used
Ans: a
117. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it
(6) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
(c) nothing will happen to motor
(d) motor will come to stop
Ans: a
118. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short
duration. We will select the
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: a
119. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: c
120. Which D.C. motor has got maximum self relieving property ?
(a) Series motor
(6) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a
121. In the D.C. motor the iron losses occur in
(a) the field
(b) the armature
(c) the brushes
(d) the commutator
Ans: b
122. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
(a) reducing the field current
(b) decreasing the armature current
(c) increasing the armature current
(d) increasing the excitation current
(e) none of the above methods
Ans: a
123. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
(a) runs as a generator
(b) does not run as a generator
(c) also runs as a motor comes to stop after sometime
Ans: a
Power system
1. An industrial consumer hall a daily load pattern of 2000 KW, 0.8 lag for 12 Hra and 1000 kW UPF for 1J Hr. The load factor i= _____.
(a) 0.5
(b) 0.75
(c) 0.6
(d) 2.0
Ans: c
2. What is the maximum value of a load which consume 500 KWh per day at a load factor of 0.40, if the consumer increases the load factor of 0.50 without increasing the maximum demand?
(a) 52.08 kW
(b) 50.8 kW
(c) 4.5 kW
(d) 60 kW
Ans: a
3. A consumer consume. 600 kWh per day at a load factor of 0.40. If the coneumer increases the load factor of 0.70 without increasing the maximum demand, what is the consumption of energy in kWh
(a) 950 kWh
(b) 1000 kWh
(c) 1050 kWh
(d) 1100 kWh
Ans: c
4. The yearly load duration curve of a power plant is a straight line. The maximum load is 750 MW and the minimum load is 600 Mw. The capacity of the plant is 900 MW. What is the capacity factor and utilization factor?
(a) 0.56,0.80
(b) 0.83,0.75
(c) 0.78, 0.9
(d) 0.75, 0.83
Ans: d
5. What is the utilization factor of a power station which supplies the following loads?
Load A: Motor load of200 kW between 10 AM to7PM
Load B : Lighting load of 100 kW between 7 PM to 11 PM
Load C : Pumping load of 110 kW between 3 PM to 10 AM
(a) 1.60
(c) 1.00
(b) 1.32
(d) 2.56
Ans: b
6. A power station supplies the peak load of 60 Mw, 40 MW and 70 MW to three localities. The annual load factor is 0.50 p.u. and the diversity factor of the load at the station is 1.55. The maximum demand on the station and average load respectively will be
(a) 120 MW, 60.8
(b) 90 MW, 50.6
(c) 103.2 MW, 51.61
(d) 100 MW, 0.51
Ans: c
7. The load duration curve for a system, is shown in the figure below. The load factor will be
[pic]
(a) 0.83
(b) 0.96
(c) 0.67
(d) 0.50
Ans: a
8. A generating station has a maximum demand of 50 Mw, a load factor of 60%, a plant capacity factor of 45% and if the plant while running as per schedule, were fully loaded. The daily energy produced will be
(a) 400 MW
(b) 720 MW
(c) 500 MW
(d) 600 MW
Ans: b
9. A generating st ation has a maximum, demand of 20 mW, load factor of 60%, a plant capacity factor of 50% and a plant
Use factor of 72%. What is the reserve capacity of the plant, if the plant, while running as per schedule, were fully loaded?
(a) 10 MW
(b) 15 MW
(c) 2 MW
(d) 5 MW
Ans: d
10. In the above question, the maximum energy that could be produced daily is
(a) 500 MWhlday
(b) 360 MWhIday
(c) 600 MWhlday
(d) 720 MWhlday
Ans: a
11. In a DC transmission line
(a) it is necessary for the sending end and receiving end to be operated in synchronism.
(b) the effects of inductive and capacitive reactances are greater than in an AC transmission line of the same rating.
(c) there are no effects due to inductive and capacitive reactances.
(d) power transfer capability is limited by stability considerations.
Ans: c
12. The impedance of a circuit is given by z=3+j4. Its conductance will be
(a) 1/3
(b) 3/5
(c) 3/25
(d) 4/5
Ans: c
13. A 100 km transmiesion line ia deaigned for a nominal voltage of 132 kV and conaiala of one conductor per phase. The line reactance is 0.726 ohm/km. The static transmission capacity of the line, in Megawatts, would be
(a) 132
(b) 240
(c) 416
(d) 720
Ans: c
14. The per unit impedance ofa circuit element is 0.15. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be
(a) 0.075
(b) 0.15
(c) 0.30
(d) 0.600
Ans: c
15. The conductor of a 10 km long, single phase, two wire line are separated by a distance of 1.5 m. The diameter of each conductor is 1 cm, If the conductors are of copper, the inductance of the circuit is
(a) 50.0 mH
(b) 45.3 mH
(c) 23.8 mH
(d) 19.6 mH
Ans: c
16. For a single phase overhead line having solid copper conductors of diameter 1 cm, spaced 60 cm between centers, the inductance in mH/km is
(a) 0.05 + 0.2 ln 60
(b) 0.2 ln 60
(c) 0.05 + 0.2 ln (6010.5)
(d) 0.2 ln (60/0.5)
Ans: c
17. A 100 km long transmission line is loaded at 110 kV.if the loss of line is 5 MW and the load is 150 MVA, the resistance of the line is
(a) 8.06 ohms per phase
(b) 0.806 ohms per phase
(c) 0.0806 ohms per phase
(d) 80.6 ohms per phase
Ans: a
18. A 3-phase, 11 kv, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance perphase of the capacitor in micro-farads is
(a) 3.948
(b) 1.316
(c) 0.439
(d) 11.844
Ans: b
19. For equilateral spacing of conductors of an untrasposed 3-phase line, we have
(a) balanced receiving end voltage and no communication interference
(b) unbalanced receiving end voltage and no communication interference
(c) balanced receiving end voltage and communication interference
(d) unbalanced receiving end voltage and communication interference.
Ans: c
20. For a 500 Hz frequency excitation, a 50 #em long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data insufficient for decision
Ans: c
21. Which one of the following statement. is not correct for the use of bundled conductors in transmission lines?
(a) Control of voltage gradient
(b) Reduction in corona 1088
(c) Reduction in radio interference
(d) Increase in interference with communication lines
Ans: d
22. The main consideration for higher and higher operating voltage of transmission is to
(a) increase the efficiency of transmission
(b) reduce power losses
(c) increase power transmission capability
(d) both (a) and (b) above
Ans: c
23. A single phaae transmisson line of impedance j 0.8 ohm supplies a resistive load of 500 A at 300 V. The sending end
power factor is
(a) unity
(b) 0.8 lagging
(c) 0.8 leading
(d) 0.6 lagging
Ans: d
24. A medium line with parameters A, B, C, D is extended by connecting a short line of impedance Z in series The overall ABCD parameteres of the series combinatton will be
(a) A, AZ, C + D/Z, D
(b) A, AZ + B, C, CZ + D
(c) A + BZ, B, C + DZ, D
(d) AZ, B, C/Z, D
Ans: b
25. When bundle conductors are used in place of single conductors, the effective inductance and capacitance will respectively
(a) increase and decrease
(b) decrease and increase
(c) decrease and remain unaffected
(d) remain unaffected and increase
Ans: c
26. To increase the visual critical voltage of cporona for an overhead line, one solid phase-conductor is replaced by a "bundle" of four smaller conductors per phase, having an aggregate cross-sectional area equal to that of the solid conductor. If the radius of the solid conductor is 40 mm, then the radius of each of the bundle conductors would be
(a) 10 mm
(b) 20 mm
(c) 28.2 mm
(d) 30 mm
Ans: d
27. For an existing ac transmision line, the string efficiency is 80%, if dc voltage is supplied for the same set up, the string efficiency will be
(a) < 80%
(b) 80%
(c) 90%
(d) 100%
Ans: b
28. In a string of suspension insulators, the voltage distribution across the different units of a string could be made uniform by the use of a grading ring, because it
(a) forms capacitances with link-pins to carry the charging current from link pins
(b) forms capacitances which help to cancel the charging current from link pins
(c) increases the capacitances of lower insulator units of cause equal voltage drop
(d) decreases the capacitances of upper insulators units to cause equal voltage drop
Ans: b
29. A three phase over head transmission line has its conductors horirzontally spaced with spacing between adjacent conductors equal to 'd'. if now the conductors of the line are rearranged to form and equilateral triangle of sides equal to 'd' then
(a) average capacitance and inductance will increase
(b) average capacitance will decrease and inductance will increase
(c) average capacitance will increase and inductance will decrease
(d) surge impedance loading of the line Increases
Ans: a
30. For a 500 Hz frequency excitation, a 50 km, long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data insufficiency for decision
Ans: c
31. If in a short transmission line, resistance and inductance are found to be equal and regulation appear. to be zero, then the load will
(a) have unity power factor
(b) have zero power factor
(c) be 0.707 lagging
(d) be 0.707 lagging
Ans: c
32. "Expanded ACSR" are conductors composed of
(a) larger diameter individual strands for a given cross-section of the aluminium strangs
(b) larger diameter of a central steel strands for a given overall diameter of the conductor
(c) larger diamter of the aluminium strands only for a given overall diameter of the conductor
(d) a fillter between the inner steel and the outer aluminium strands to increase the overall diameter of the conductor
Ans: d
33. What is the sag for a span of 400m, if the ultimate tensile strength of conductor is 6000 kgf, and the weight of conductor is 550 kgf/km? Factor of safety is 2.
(a) 1.016 m
(b) 2.40 m
(c) 3.6 m
(d) 4.2 m
Ans: c
34. A transmission line haB a span of 275 m between level supporte. The conductor has a diameter of 19.58 mm, weight 0.844 kgpm and has an ultimate breaking strength of 7950 kgf. Each conductor has a radial covering of ice 9.58 mm thick and is subjected to a horizontal wind pressure of 40 k617m2 of ice covering projected area. If the factor of safety is 2, what is the deflected sag? Ice weight is 913.5 kg/m3
(a) 5.36
(b) 4.1 m
(c) 3.9 m
(d) 3.01 m
Ans: a
35. A transmission line conductor having a diameter of 19.5 mm, weight 850 kglkm. The span is 275 m. The wind pressure is 39 kg/m of projected area with ice coating of 13 mm. The ultimate strength of the conductor is'8000 kg. What is the maximum sag, if the factor of safety is 2 and ice weight 910 kg/m3?
(a) 4.5 m
(b) 6.4 m
(c) 7.0 m
(d) 5 m
Ans: b
36. A transmission line conductor at a river crossing is supported from two towers at height. of 30 m and 90m, above water level. The horizontal distance between the towers is 270m, if the tension in the conductor is 1800 kg and the conductor weight 1 kg/m. What is the clearance between the conductor and the water at a point midway between the towers?
(a) 79.50 m
(b) 54.94 m
(c) 60 m
(d) 51.4 m
Ans: b
37. An overhead transmission line has a span of 240m between level supports. What is the maximum sag if the conductor weight 727 kg/km and has a breaking strength of 6880 kg? Allow the factor of safety of 2. Neglecting wind and ice loading.
(a) 1.52 m
(b) 1.6 m
(c) 0.75 m
(d) 1.25 m
Ans: a
38. The line conductor of a transmission line has an overall diameter of 19.53 mm, weight 0.844 kg/m and an ultimate breaking strength of 7950 kg. If the factor of safety is to be 2, when conductor has an ice of 1 kg/m and a horizontal wind pressure of 1.5 kg/m. What is the vertical sag, corresponding to this loading for a 300 m span level supports?
(a) 1.08 m
(b) 5.0 m
(c) 5.22 m
(d) 4.62 m
Ans: c
39. A two conductor 1 - pi line operates at 50 Hz. The diameter of each conductor is 20 mm and the spacing between conductors is 3m. What is the inductance of each conductor per km?
(a) 1.19 kH/km
(b) 1.24 mH/km
(c) 2.38 mH/km
(d) 0.59 mH/km
Ans: a
40. A two conductor 1 - pi line operates at 50 Hz. The diameter of each conductor is 20mm and the spacing between conductor is 3m. When the conductor material is steel of relative permeability 50, the loop inductance per km of the line will be
(a) 8.2 mHlkm
(b) 7.281 mHlkm
(c) 5.0 mHlkm
(d) 2 mHlkm
Ans: b
41. A 1-pi line two conductors operate at 50Hz. The diameter of each conductor is 15 mm, and the spacing between the conductor is 3.5 m. The inductive reactance per km will be
(a) 0.43 ClIkm
(b) 0.65 0Jkm
(c) 0.70 O/km
(d) 0.79 nIkm
Ans: d
42. A conductor is composed of seven identical copper .Iranu, each having a radius r. The self GMD of the conductors will be
(a) 2.177 r
(b) 2.645 r
(c) 2.141 r
(d) 1.21 r
Ans: a
43. The charging current per kill of the line is
(a) 0.497 Amp
(b) 0.61 Amp
(c) 0.68 Amp
(d) 0.21 Amp
Ans: a
44. What is the time of operation of a relay of rating 5 amp 2.2 sec, IDMT and having a relay of setting of 125% Tms = 0.6 It is connected to a supply circuit through a CT, 400 ratio. The fault current is 400 amp.
(a) 10.Osec
(b) 1.92sec
(c) 4.5 sec
(d) 2.4 sec
Ans: b
45. A two conductor 1 - pi line operates at 50 Hz. The diameter of each conductor is 2 cm and are spaced 3m apart. What is the line to line capacitance
(a) 9.74 x 10-9 F/km
(b) 4.87 x 10-9 F/km
(c) 3.05 x 10-9 F/km
(d) None of these
Ans: b
46. A two conductor 1 - pi line operates at 50 Hz.
The diameter of each conductor is 4 cm and are spaced 6 m apart. What is the capacitive susceptance to neutral per km?
(a) 1.42 x 10-9 s/km
(b) 3.25 x 10-8 s/km
(c) 4.8 x 10-9 s/krn
(d) 3.06 x 10-9 s/km
Ans: d
47. A three phase 50 Hz line consists of three conductors each of diameter 21 mm, The spacing between the conductors all follows:
A - B = 3m, B - C = 5m, C - A = 3.6m
If the line operates at 132 k V, the reactive voltampere generatd by the line per km is
(a) 51.07 kVAr
(b) 51.70 kVAr
(c) 40.0 kVAr
(d) 60.5 kVAr
Ans: b
48. A two conductor 1 - pi line operates at 50 Hz.
The diameter of each conductor is 20 mm and the spacing between the conductors is 3m, The height of conductor above the ground is 6 m. The capacitance of the line to neutral will be
(a) 9.7 pF/m
(b) 10.2 pF/m
(c) 8.7 uF/km
(d) 2.4 uF/m
Ans: a
49. For a 500 Hz frequency excitation, a 50 km long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data isufficient decision
Ans: c
50. Bundled conductors are employed to
(a) reduce the short circuit current
(b) improve system stability
(c) decreases system stability
(d) increase the short circuit current
Ans: c
51. Series capacitive compensation in EHV transmission lines is used to
(a) reduce the line loading
(b) improve the stability of the system
(c) reduce the voltage profile
(d) improve the protection of the line
Ans: b
52. A lossless radial tranemission line with surge impedance loading
(a) takes negative VAr at sending end and zero VAr at receiving end
(b) takes positive VAr at sending end and zero VAr at receiving end
(c) has flat voltage profile and unity power factor at all points along it
(d) has sending end voltage higher than receiving end voltage and unity power factor at sending end
Ans: a
53. The X:R ratio of 220 kV line as compared to 400 kV line is
(a) greater
(b) smaller
(c) equal
(d) it could be anything
Ans: b
54. If a line is 100 % series compensated it may result into series resonance at power frequency of
(a) 50 Hz
(c) 150 Hz
(b) 100 Hz
(d) none of the above
Ans: a
55. A 60 Hz, 320 km loesless line has Bending end voltage 1.0 p.u, The receiving end voltage on no load is
(a) 1.1 p.u.
(b) 1.088 p.u.
(c) 1.116 p.u.
(d) none of the above
Ans: b
56. With 100 % series compensation of line.
(a) the circuit is series resonant at power frequency
(b) low transient voltage
(c) high transient current
(d) both (a) and (c)
Ans: d
57. For certain geometry and operating voltage of the uncompensated transmission line, the ratio of power transfer capability to the surge inpedance loading with increase in length
(a) increases
(b) remains unchanged
(c) decreases
(d) uncertain
Ans: c
58. The effect of series capacitance compensation is
(a) to decrease the virtual surge impedance
(b) to decrease the effective length of the line
(c) to increase virtual surge impedance loading
(d) all of the above
Ans: d
59. For a long uncompensatedline the limit to the line loading ill governed by
(a) thermal limit
(b) voltage drop
(c) stability limit
(d) corona loss
Ans: c
60. For any fixed degree of inductive shunt compensation, additional series capacitive compensation
(a) increase the effective length of line
(b) increase virtual surge impedance line
(c) decrease virtual surge impedance loading of the line
(d) none of the above
Ans: d
61. With 100 % inductive shunt compensation, the voltage profile is flat for
(a) 100 % loading of line
(b) 50 % loading of line
(c) zero loading of line
(d) none of the above
Ans: c
62. A loss less line terminated with its surge impedance has
(a) flat voltage profile
(b) transmission line angle is greater than actual length of line
(c) transmission line agnle is less than the actual length
(d) both (a) and (b) above
Ans: a
63. For reducing tower footing resistance it is better to Use
(a) chemical and ground rods only
(b) chemical and counterpoise only
(c) ground rod and counterpoise only
(d) chemical, ground rods and counterpoise
Ans: c
64. An RLC series. circuit remains predominantly inductive
(a) at resonance frequency
(b) below resonance frequency
(c) above resonance frequency
(d) at the lower half power frequency
Ans: c
65. The corona loss on a particular system at 50 Hz is 1 kw/phase per km. The corona loss on the same system with supply frequency 25 Hz will be
(a) 1 kW/phase/km
(b) 0.5 kW/phase/km
(c) 0.667 kW/phase/km
(d) none of the above
Ans: c
66. A voltage of 1000 kV is applied to an overhead line with its receiving end open. If the surge impedance of the line is 500 ohm, then the total surge power in the line ill
(a) 2000 MW
(b) 500 MW
(c) 2 MW
(d) 0.5 MW
Ans: a
67. The main criterion for selection of the size of a distribution for a radial distribution system is
(a) voltage drop
(b) corona loss
(c) temperature rise
(d) capital cost
Ans: a
68. If an induction machine is run at above synchromous speed, it acts as
(a) a synchronous motor
(b) an indcution generator
(c) an inductor motor
(d) none of the above
Ans: b
69. The low voltage winding of a 400/230 V, 1-phase, 50 Hz transformer is to be connected to a 25 Hz, the supply voltage should be
(a) 230 V
(b) 460 V
(c) 115 V
(d) 65 V
Ans: c
70. Corona losses are minimized when
(a) conductors size is reduced
(b) smooth conductor is reduced
(c) sharp points are provided in the line hardware
(d) current density in conductors is reduced
Ans: b
71. The order of the sub-harmonic during SSR for 50 Hz nornal frequency is
(a) 25 Hz
(b) 16 2/3 Hz
(c) 10 HZ
(d) none of the above
Ans: d
72. The non-uniform distribution of voltage across the units in a string of suspention type insulators is due to
(a) unequal self-capacitance of the units
(b) non-uniform distance of separation of the units from the tower body
(c) the existence of stray capacitance between the metallic junctions of the units and the tower body
(d) non-uniform distance between the cross-arm and the units
Ans: c
73. Whenever the conductors are dead-ended of there is a change in the direction of transmission line, the insulator. used are of the
(a) pin type
(b) suspension type
(c) strain type
(d) shackle type
Ans: c
74. The time taken for a surge to travel a 600 km long overhead transmission line is
(a) 6s
(b) 1s
(c) 0.02s
(d) 0.002s
Ans: d
75. The function of the earth wire in an extra high voltage line is to
(a) prevent earth fault
(b) provide a safety measure for any high-flying object
(c) provide a shield to the phase con-ductors from direct lightning stroke
(d) provide mechanical strength to the towers
Ans: c
76. A long overhead transmission line is terminated by its characteristic impedance. Under this operating condition, the ratio of the voltage to the current at different points along the line will
(a) progressively increase from the sending-end to the receiving end
(b) progresively increase from the receiving end to the sending-end
(c) remain the same at the two ends, but be higher between the two ends being maximumat the centre of the line
(d) remain the same at all points
Ans: b
77. For a transmission line with negligible losses, the lagging reactive power (VAR) delivered at Ihe receiving end, for a given receiving end voltage, is directly proportional to the
(a) square of the line voltage drop
(b) line voltage drop
(c) line inductive reactance
(d) line capacitive reactance
Ans: b
78. Corona loss can be reduced by the use of hollow conductors because
(a) the current density is reduced
(b) the eddy current in the conductor is eliminated
(c) for a given cross-section, the radius of the conductor is increased
(d) of better ventilation in the conductor
Ans: d
79. The insulation of modern EHV lines is designed based on
(a) the lightning voltage
(b) corona
(c) radio interface
(d) switching voltage
Ans: d
80. Shunt conapenBation in an EHV line is "Bed
(a) improve stability
(b) reduce fault level
(c) improve the voltage profile
(d) subsitute for synchronous phase modifier
Ans: d
81. In a 3-core extra-high voltage cable, a metallic screen around each core¬i,..ulation i. provided to
(a) facilitate heat dissipation
(b) give mechanical strength
(c) obtain radial electric stress
(d) obtain longtiudinal electric stress
Ans: c
82. The aingle pbase line of 280 V and 3 pha.e line of 400 V which feed different domestic circuit. and induetrial loade represent
(a) primary distribution
(b) secondary distribution
(c) secondary transmission
(d) none of the above
Ans: b
83. The transmission line feeding power on either side of the main transmission line i. called
(a) Secondary distribution
(b) Secondary transmission
(c) Primary transmission
(d) Primary distribution
Ans: b
84. Series capacitive compensation on EHV transmission lines is used to
(a) reduce the line loading
(b) improve the stability of the system
(c) reduce the voltage profile
(d) improve the protection of the line
Ans: d
85. At a particular unbalanced node, the real powers specified are Leaving the node : 20 Mw, 25 Mw, Entering the node: 60 Mw, 30 MW. The balance power will be
(a) 30 MW leaving the node
(b) 45 MW leaving the node
(c) 45 MW entering the node
(d) 22.5MW entering the node and 22.5 MW leaving the node
Ans: b
86. When a d.c source is switched is purely inductive, the current response is
(a) an exponentially rising curve
(b) an exponentially decaying curve
(c) a straight line passing through the origin
(d) a straight line off-set from the origin
Ans: c
87. If transformer frequency is changed from 60 Hz, to 60 Hz the ratio of eddy current loss 60 Hz to 50 Hz, at constant voltage will be
(a) 5/6
(b) 25/36
(c) 6/5
(d) 1.0
Ans: d
88. In load flow analysis, the load connected at a bUs is represented as
(a) constant current drawn from the bus
(b) constant impedance connected at the bus
(c) voltage and frequency dependent source at the bus
(d) constant real and reactive drawn from the bus
Ans: d
89. If the reference bUB is changed in two load flow runs with same Bystena data and power obtained for reference bur taken a. specified P and Q in the latter run
(a) the system losses will be unchanged but complex bus voltage will change
(b) the system losses will be changed but complex bus voltages remain unchanged
(c) the system losses as well be as complex bus voltage will change
(d) the system losses as well be as complex bus voltage will unchange
Ans: a
90. A square matrix is called singular if its
(a) determina is unity
(b) determinant is zero
(c) determinant is infinity
(d) rank is unity
Ans: b
91. Gauss-Seidel iterative method can be used for solving a set of
(a) linear differential equations only
(b) linear algebraic equation only
(c) both linear and nonlinear algebraic equations
(d) both linear and nonlinear differential equations
Ans: b
92. Pure inductive circuit takes power (reactive) from the a.c. line when
(a) both applied voltage and current rise
(b) both applied voltage anti current decrease
(c) applied voltage decreases but current Increases
(d) none of these
Ans: b
93. An alternator has a phase sequence of RYB for itB phase voltage. In case offield current is reversed, the phase sequence will become
(a) RBY
(b) RYB
(c) YRB
(d) none of these
Ans: b
94. An alternator has a phase sequence of RYB for its phase voltage. In case the direetior of rotation of alternator is reversed, the phase sequence will become
(a) RBY
(b) RYB
(c) YRB
(d) none of these
Ans: a
95. A synchronous generator connected to an infinite bUB delivers power at a lag p.r. If its excitation is increased
(a) the terminal voltage increases
(b) voltage angle 8 increases
(c) current delivered increases
(d) all of the above
Ans: c
96. A synchronous motor connected to an infinite bUB takes power at a lag p.f. If its excitation is increased
(a) the terminal voltage increases
(b) the load angle increases
(c) the p.f. of motor increases
(d) all of the above
Ans: c
97. A star-conneted 440 V, 50 Hz alternator has per phase synchronous reactance of 10 n. It supplies a bal anced capacitive load current of 20 A, as shown in per phase equivalent circuit of the given figure. It is desirable to have zero voltage regulation. The load power factor should be
(a) 0.82
(b) 0.47
(c) 0.39
(d) 0.92
Ans: a
98. A 10k VA, 400 V/200 V single phase transformer with 10 % impedance draws a steady short circuit line current of
(a) 50 A
(b) 150 A
(c) 250 A
(d) 350 A
Ans: b
99. The percentage resistance and percentage reactance of a 10 kVA, 400 V/200 V, 3-phase transformer are 2% and 10% respectively. If the constant losses in the machine are 1 %, the maximum possible percentage efficiency of the transformer is
(a) 98.32
(b) 97.25
(c) 96.85
(d) 96.12
Ans: c
100. The voltage of CI generator and an infinite bus are given as O.92LIO 0 and 1.0L'O 0 respectively. The active power will flow from
(a) generator to infinite bus
(b) infinite bus to generator
(c) the data is insufficient to judge
(d) none of the above
Ans: a
101. In case ora 3 phase short circuit in a system the power fed into the system is
(a) mostly reactive
(b) mostly active
(c) active and reactive both equal
(d) reactive only
Ans: a
102. With the help of a reactive compensator it is possible to have
(u) constant voltage opei ation only
(b) unity p.f. operation only
(c) both constant voltage and unity p.f.
(d) either constant voltage or unity p.f.
Ans: d
103. For a long uncompensated line the limit to the line loading is governed by
(a) thermal limit
(b) voltage drop
(c) stability limit
(d) corona loss
Ans: c
104. A shunt reactor at 100 MVAr is operated at 98% of its rated voltage and at 96% of its rated frequency. The reactive power absorbed by the reactor is
(a) 98 MVAr
(b) 104.02 MVAr
(c) 96.04 MVAr
(d) 100.04 MVAr
Ans: d
105. A 100 kVA transformer has 4% impedance and 50 k VA transformer has 3% impedance when they are operated in parallel, which 6 transformer will reacb full load first
(a) 3%
(b) 4%
(c) data is insufficient
(d) none of the above
Ans: a
1. Basic source of magnetism ______________.
(a) Charged particles alone (b) Movement of charged particles
(c) Magnetic dipoles (d) Magnetic domains
Ans:- b
2. Units for magnetic flux density
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m
Ans:- a
3. Magnetic permeability has units as
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m
Ans:- b
4. Magnetic permeability has units as
(a) Tesla (b) Henry (c) Tesla / m (d) Henry / m
Ans:- d
5. Magnetic field strength’s units are
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m
Ans:- c
6. Example for dia-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites
Ans:- a
7. Example for para-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites
Ans:- b
8. Example for ferro-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites
Ans:- c
9. Example for anti-ferro-magnetic materials
(a) salts of transition elements (b) rare earth elements (c) transition metals (d) Ferrites
Ans:- a
10. Example for ferri-magnetic materials
(a) salts of transition elements (b) rare earth elements (c) transition metals (d) Ferrites
Ans:- d
11. Magnetic susceptibility para-magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2
Ans:- d
12. Magnetic susceptibility dia--magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2
Ans:- b
13. Magnetic susceptibility ferro-magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2
Ans:- c
14. Typical size of magnetic domains ______ (mm).
(a) 1-10 (b) 0.1-1 (c) 0.05 (d) 0.001
Ans:- c
15. Typical thickness of Bloch walls ______ (nm).
(a) 0.1-1 (b) 1-10 (c) 10-50 (d) 100
Ans:- d
16. Example for soft magnet
(a) 45 Permalloy (b) CrO2 (c) Fe-Pd (d) Alnico
Ans:- a
17. Example for hard magnet
(a) 45 Permalloy (b) CrO2 (c) Fe-Pd (d) Alnico
17. d
18. Example for magnetic material used in data storage devices
a) 45 Permalloy (b) CrO2 (c) Cunife (d) Alnico
Ans:- b
Q.1 Materials which can store electrical energy are called
(A) magnetic materials. (B) semi conductors.
(C) dielectric materials. (D) super conductors.
Ans: C
Q.2 ACSR (Aluminium Conductor Steel Reinforced) are used as
(A) over head transmission lines. (B) super conductors.
(C) fuse (D) underground cables.
Ans: A
Q.3 Brass is an alloy of
(A) copper and zinc. (B) copper and iron.
(C) copper and Aluminium. (D) copper and tin.
Ans: A
Q.4 Property of material which allows it to be drawn out into wires is
(A) Ductility. (B) Solder ability.
(C) Super conductivity. (D) Malleability.
Ans: A
Q.5 In n type semi conductor added impurity is
(A) pentavalent. (B) divalent.
(C) tetravalent. (D) trivalent.
Ans: A
Q.6 The covers of electrical machines are made of
(A) soft magnetic materials. (B) hard magnetic materials.
(C) super conductors. (D) semiconductors.
Ans: A
Q.7 The dielectric constant of air is practically taken as
(A) more than unity. (B) unity.
(C) less than unity. (D) zero.
Ans: B
Q.8 n-type semiconductor is an example of
(A) extrinsic semiconductor. (B) intrinsic semiconductor.
(C) super conductor. (D) insulators..
Ans: A
Q.9 Atomic weight of an atom is
(A) sum of the number of protons and neutrons.
(B) sum of the number of protons and electrons.
(C) sum of the number of electrons and neutrons.
(D) sum of the number of electrons, protons and neutrons.
Ans: A
Q.10 Gold and silver are
(A) dielectric materials
(B) low resistivity conducting materials.
(C) magnetic materials.
(D) insulating materials.
Ans: B
Q.11 Phenol and Formaldehyde are polymerised to a resultant product known as
(A) PVC. (B) bakelite.
(C) polyester. (D) teflon.
Ans: B
Q.12 Dielectric materials are
(A) Insulating materials. (B) Semiconducting materials.
(C) Magnetic materials. (D) Ferroelectric materials.
Ans: A
Q.13 Thermocouples are used for the measurement of
(A) humidity. (B) pressure.
(C) temperature. (D) density.
Ans: C
Q.14 Large scale integration chips have between
(A) Less than 10 components. (B) 10 and 100 components.
(C) 100 and 1000 components. (D) More than 1000 components.
Ans: C
Q.15 All semiconductors in their last orbit have
(A) 8 electrons. (B) 2 electrons.
(C) 4 electrons. (D) 6 electrons.
Ans: C
Q.16 The material with lowest resistivity is
(A) constantan. (B) silver.
(C) manganin. (D) nichrome.
Ans: B
Q.17 The property due to which the resistance of some metal or compound vanishes under certain
conditions is
(A) Semi conductivity. (B) Super conductivity.
(C) Curie point. (D) Magnetostriction.
Ans: B
Q.18 Bronze is an alloy of
(A) copper. (B) aluminium.
(C) silver. (D) carbon.
Ans: A
Q.19 Ceramics are good
(A) insulators. (B) conductors.
(C) superconductors. (D) semiconductors.
Ans: A
Q.20 The critical temperature above which the ferromagnetic materials loose their magnetic
property is known as
(A) hysterisis. (B) Curie point.
(C) transition temperature. (D) standard temperature.
Ans: B
Q.21 Permanent magnets are made of
(A) soft magnetic materials. (B) hard magnetic materials.
(C) semi conductors. (D) super conductors.
Ans: B
Q.22 Holes are majority carriers in
(A) P-type semiconductors. (B) N-type semiconductors.
(C) Insulators. (D) Superconductors.
Ans: A
Q.23 Materials, which provide a path to the magnetic flux, are classified as
(A) insulating materials. (B) semi conducting materials.
(C) magnetic materials. (D) dielectric materials.
Ans: C
Q.24 Germanium possesses
(A) one valence electrons. (B) two valence electrons.
(C) three valence electrons. (D) four valence electrons.
Ans: D
Q.25 Dielectric constant of vacuum is
(A) infinity. (B) 100.
(C) one. (D) zero.
Ans: C
Q.26 Ferrites are
(A) ferromagnetic material. (B) ferrimagnetic materials.
(C) anti ferromagnetic material. (D) diamagnetic materials.
Ans: A
Q.27 The relative permeability of a paramagnetic substance is
(A) unity. (B) slightly more than unity.
(C) zero. (D) less than unity.
Ans: B
Q.28 Hall effect may be used for which of the following?
(A) determining whether the semiconductor is p or n type.
(B) determining the carrier concentration.
(C) calculating the mobility.
(D) All the above.
Ans: D Determining whether the semiconductor is p or n type, determining the carrier
concentration, calculating the mobility.
Q.29 Manganin is an alloy of
(A) copper, manganese and nickel. (B) copper and manganese.
(C) manganese and nickel. (D) manganese, aluminium and nickel.
Ans: A
Q.30 Eddy current loss is proportional to the
(A) frequency. (B) square of the frequency.
(C) cube of the frequency. (D) square-root of the frequency.
Ans: B
Q.31 A pure semiconductor under ordinary conditions behaves like
(A) a conductor. (B) an insulator.
(C) a magnetic material. (D) a ferro-electric material.
Ans: B
Q.32 In p-type semiconductor the majority carriers are
(A) holes. (B) electrons.
(C) positive ions. (D) negative ions.
Ans: A
Q.33 Copper is completely miscible with
(A) nickel. (B) gold.
(C) hydrogen. (D) lead.
Ans: B
Q.34 For germanium the forbidden gap is
(A) 0.15ev. (B) 0.25ev.
(C) 0.5ev. (D) 0.7ev.
Ans: D
Q.35 The dielectric strength of transformer oil should be
(A) 100 V. (B) 5 KV.
(C) 30 KV. (D) 132 KV.
Ans: C
Q.36 Resistivity of conductors is most affected by
(A) composition. (B) temperature.
(C) pressure. (D) current.
Ans: B
Q.37 Copper constantan is used for measuring temperature upto
(A) 1400 C
. (B) 1100 C
.(C) 800 C
. (D) 400 C
.Ans: D
Q.38 Mica is a
(A) Dielectric material. (B) Insulating material.
(C) Magnetic material. (D) Both insulating and dielectric
material.
Ans: D
Q.39 The conductivity of copper is less than that of silver by
(A) 5 – 10 %. (B) 50 – 60 %.
(C) 80 – 90 %. (D) 20 – 30 %.
Ans: A
Q.40 A ferrite core has less eddy current loss than an iron core because ferrites have
(A) High resistance. (B) Low resistance.
(C) Low permeability. (D) High hysteresis.
Ans: A
Q.41 Transformer cores are laminated with
(A) Low carbon steel. (B) Silicon sheet steel.
(C) Nickel alloy steel. (D) Chromium sheet steel.
Ans: B
Q.42 For silicon the forbidden gap is
(A) 1.1ev. (B) 0.25ev.
(C) 0.5ev. (D) 0.7ev.
Ans: A
Q.43 Plastics are
(A) Good conductors of heat. (B) Good conductors of electricity.
(C) Bad conductors of electricity. (D) High density.
Ans: C
Q.44 In order to obtain p-type germanium it should be doped with a
(A) Trivalent impurity. (B) Tetravalent impurity.
(C) Pentavalent impurity. (D) Any of the above will do.
Ans: A
Q.45 Barrier potential in a P-N junction is caused by
(A) Thermally generated electrons and holes.
(B) Diffusion of majority carriers across the junction.
(C) Migration of minority carriers across the junction.
(D) Flow of drift current.
Ans: B
Q.46 The heating elements of electric irons are made of
(A) Copper. (B) Nichrome.
(C) Constantan. (D) Aluminium.
Ans: B
Q.47 The most malleable, ductile low resistivity material is
(A) Copper. (B) Aluminium.
(C) Silver. (D) Iron.
Ans: C
Q.48 The percentage of carbon in mild steel is
(A) 0.08 to 0.3 % (B) 0.5 to 1.4 %
(D) 2.35 % (D) 0.5 %
Ans: A
Q.49 Aluminium is
(A) Silvery white in colour. (B) Yellow in colour.
(C) Reddish in colour. (D) Pale yellow in colour.
Ans: A
Q.50 Hard ferrites are used for making
(A) Transformer cores. (B) Electrical machinery.
(C) High frequency equipment. (D) Light weight permanent magnets.
Ans: D
Q.51 The main constituents of glass is
(A) SiO2 (B) B2O3
(C) Al2O3 (D) Cr2O3
Ans: A
Q.52 Micanite is a form of
(A) Built up mica.
(B) Hydrated potassium aluminium silicate.
(C) Magnesium mica.
(D) Calcium mica.
Ans: A
Q.53 What is the type of bonding in silicon?
(A) Ionic. (B) Covalent.
(C) Metallic. (D) Ionic + Metallic
Ans: B
Q.54 P-N junction is
(A) a rectifier. (B) an amplifier.
(C) an Oscillator. (D) a Coupler.
Ans: A
Q.55 The conductivity of an extrinsic semiconductor
(A) decreases with temperature.
(B) increases with temperature.
(C) remains constant with temperature.
(D) decreases and then increases with temperature.
Ans: B
Q.56 When a semiconductor is doped with a P-type impurity, each impurity atom will
(A) acquire negative charge. (B) acquire positive charge.
(C) remain electrically neutral. (D) give away one electron.
Ans: A
Q.57 Number of Terminals in a MOSFET are
(A) Two (B) Three
(C) Four (D) Five
Ans: B
Q.58 Which of the following material has the highest melting point
(A) Copper. (B) Aluminium.
(C) Tungsten. (D) Gold.
Ans: C
Q.59 Bronze is an alloy of
(A) Copper and Tin. (B) Copper and Steel.
(C) Copper and Mercury. (D) Copper and Aluminium.
Ans: A
Q.60 A transistor has
(A) One p-n junction. (B) Two p-n junction.
(C) Four p-n junction. (D) Five p-n junction.
Ans: B
Q.61 Example of high resistivity material is
(A) Nichrome (B) Silver
(C) Gold (D) Copper
Ans: A
Q.62 Hard magnetic materials are used for making
(A) Permanent magnets. (B) Temporary magnets.
(C) Conductors. (D) Insulator.
Ans: A
Q.63 Hall effect is associated with
(A) Conductors. (B) Semiconductors.
(C) Thermistors. (D) Solders.
Ans: B
Q.64 Addition of trivalent impurity to a semiconductor creates many
(A) holes. (B) free electrons.
(C) valance electrons. (D) bound electrons.
Ans: B
Q.65 Magnetic materials
(A) provide path to magnetic flux. (B) are good insulators.
(C) are semiconductors. (D) None.
Ans: A
Q.66 In a ferromagnetic material the state of flux density is as follows when external magnetic
field is applied to it.
(A) Increased (B) Decreased
(C) Remains unchanged (D) Becomes zero
Ans: C
Q.67 Paper is hygroscopic and absorbent.
(A) True (B) False
Ans: A
Q.68 Insulators have
(A) A full valence band. (B) An empty conduction band.
(C) A large energy gap. (D) All the above.
Ans: C
Q.69 Hysteresis loss least depends on
(A) Frequency. (B) Magnetic field intensity.
(C) Volume of the material. (D) Grain orientation of material.
Ans: D
Q.70 Atoms with four valence electrons are good conductors.
(A) True (B) False
Ans: B
Q.71 Semi-conductors have ________ temperature coefficient of resistance.
(A) Negative (B) Positive
(C) Both positive and negative (D) None of the above
Ans: A
Q.72 Tick off the material, which is different from the group
(A) Constantan. (B) Manganin.
(C) Nichrome. (D) Brass.
Ans: D
Q.73 Tick of the property, which is different from the group
(A) Ductility. (B) Resistivity.
(C) Tensile strength. (D) Hardness.
Ans: B
Q.74 Ferroelectric materials are characterised by
(A) Very high degree of polarisation.
(B) A sharp dependence of polarisation on temperature.
(C) Non-linear dependence of the charge Q on the applied voltage.
(D) All the above.
Ans: D
1. If two meters X and Y requires 40mA and 50mA respectively, to give full scale deflection, then:
a) X is more sensitive
b) Y is more sensitive
c) Both X and Y are equally sensitive
d) It would not be possible to access the sensitivity on the basis of the given data
(1) Instrument is a device for determining
(a) the magnitude of a quantity
(b) the physics of a variable
(c) either of the above
(d) both (a) and (b)
(2) Electronic instruments are preferred because they have
(a) no indicating part
(b) low resistance in parallel circuit
(c) very fast response
(d) high resistance in series circuit
(e) no passive elements.
(3) A DC wattmeter essentially consist of
(a) two ammeters
(b) two voltmeters
(c) a voltmeter and an ammeter
(d) a current and potential transformer
(4) Decibel is a unit of
(a) power
(b) impedance
(c) frequency
(d) power ratio
(5) A dc voltmeter may be used directly to measure
(a) frequency
(b) polarity
(c) power factor
(d)power
(6) An accurate voltmeter must have an internal impedance of
(a) very low value
(b) low value
(c) medium value
(d) very high value
(7) The insulation resistance of a transformer winding can be easily measured with
(a) Wheatstone bridge
(b) megger
(c) Kelvin bridge
(d) voltmeter
(8) A 100 V voltmeter has full-scale accuracy of 5%. At its reading of 50 V it will give an error of
(a) 10%
(b) 5%
(c) 2.5%
(d) 1.25%
(9) You are required to check the p. f. of an electric load. No p.f. meter is available. You would use:
(a) a wattmeter
(b) a ammeter, a voltmeter and a wattmeter
(c) a voltmeter and a ammeter
(d) a kWh meter
(10) The resistance of a field coil may be correctly measured by using
(a) a voltmeter and an ammeter
(b) Schering bridge
(c) a Kelvin double bridge
(d) a Maxwell bridge
(11) An analog instrument has output
(a) Pulsating in nature
(b) Sinusoidal in nature
(c) Which is continuous function of time and bears a constant relation to its input
(d) Independent of the input quantity
(12) Basic charge measuring instrument is
(a) Duddel's oscillograph
(b) Cathode ray oscillograph
(c) Vibration Galvanometer
(d) Bailastic Galvanometer
(e) Battery Charging equipment
(13) A.C. voltage can be measured (using a d.c. instrument) as a value obtained
(a) by subtracting the d.c. reading from it's a.c. reading.
(b) Using the output function of the multimeter
(c) By using a suitable inductor in series with it
(d) By using a parallel capacitor with it
(e) None of the above
(14) A moving coil permanent magnet ammeter can be used to measure
(a) D. C. current only
(b) A. C. current only
(c) A. C. and D. C. currents
(d) voltage by incorporating a shunt resistance
(e) none of these
(15) Select the wrong statement
(a) the internal resistance of the voltmeter must be high
(b) the internal resistance of ammeter must be low
(c) the poor overload capacity is the main disadvantage of hot wires instrument
(d) the check continuity with multimeter, the highest range should be used.
(e) In moving iron voltmeter, frequency compensation is achieved by connecting a capacitor across its fixed coil.
(16) Which of the following instrument is suitable for measuring both a.c. and d.c.
quantities.
(a) permanent magnet moving coil ammeter.
(b) Induction type ammeter.
(c) Quadrant electrometer.
(d) Moving iron repulsion type ammeter.
(e) Moving iron attraction type voltmeter.
(17) Swamping resistance is used in moving coil instruments to reduce error due to
(a) thermal EMF
(b) temperature
(c) power taken by the instrument
(d) galvanometer sensitivity.
(18) A power factor meter is based on the principle of
(a) electrostatic instrument
(b) Electrodynamometer instrument
(c) Electro thermo type instrument
(d) Rectifier type instrument.
(19) A potentiometer recorder is used for
(a) AC singles
(b) DC signals
(c) both (a) and (b)
(d) time varying signals
(e) none of these.
(20) Transformers used in conjunction with measuring instruments for measuring purposes are called
(a) Measuring transformers
(b) transformer meters
(c) power transformers
(d) instrument transformers
(e) pulse transformers.
Measurement and Instrumentation MCQ
1. If two meters X and Y requires 40mA and 50mA respectively, to give full scale deflection, then:
a) X is more sensitive
b) Y is more sensitive
c) Both X and Y are equally sensitive
d) It would not be possible to access the sensitivity on the basis of the given data
2. The reliability of the instrument refer to:
a) Measurement of changes due to temperature variations
b) Degree to which repeatability continues to remain within specified limits
c) The life of the instrument
d) The extent to which the characteristics remain linear
3. The damping torque must operate only when the moving system of the indicating instrument is:
a) Actually moving
b) Stationary
c) Just starting to move
d) Near its full deflection
4. If a voltmeter is connected, like an ammeter in series to the load:
a) The measurement reading will be too high
b) Almost no current will flow in the circuit
c) The meter will burn
d) An instantaneously high current will flow
5. Preferred material for permanent magnet is:
a) Stainless steel
b) Alnico
c) Tungsten steel
d) Soft iron
6. Air friction damping is used in the instruments which is:
a) Moving iron
b) Moving coil
c) Induction
d) Hot wire
7. PMMC instrument gives uniform scale because:
a) It uses spring control
b) It uses eddy current damping
c) The deflection torque is proportional to the instrument current
d) Both (a) and (c)
8.An instrument that is capable of measuring only dc is:
a) Moving coil
b) Moving iron
c) Thermo couple
d) None of the above
9. Maxwell-Wien bridge is used to measure:
a) Inductance
b) Capacitance
c) Dielectric loss
d) Frequency
10.A ballistic galvanometer is used to measure:
a) Charge
b) Current
c) Voltage
d) Frequency
Instrumentation MCQ Objectives
1. A thermo-couple instrument can be used for the measurement of:
a) Direct current only
b) Alternating current only
c) Both direct current and alternating current
d) dc/ac voltage only
2. Electrostatic type instruments are mainly used for measurement of:
a) Heavy currents
b) Low currents
c) Low voltages
d) High voltages
3. The instrument which is cheapest for dc measurement is:
a) Moving iron
b) PMMC
c) Hot-wire
d) Electro-dynamo
4. Measurement range of a voltmeter can be extended by using:
a) High current resistance
b) High series resistance
c) Low shunt resistance
d) Low series resistance
5. Which of the following voltmeter have least power consumption:
a) Moving iron
b) Hot-wire
c) Electrostatic
d) Induction type
6. Which of the following instruments have least torque/weight ratio:
a) Dynamometer type
b) PMMC
c) Attraction type moving iron
d) Repulsion type moving iron
7. The instrument having its deflection depends upon average value is:
a) Moving iron
b) Hot wire
c) Rectifier type
d) Induction type
8. Which of the following instruments can be used for full scale deflection of 300o:
a) PMMC
b) Induction type
c) Hot wire
d) Electrostatic
9.While testing cables the galvanometer used should be initially short-circuited in order to protect it from sudden initial inrush currents as the cable have:
a) A low value of initial resistance
b) A low value of initial capacitance
c) A high value of initial capacitance
d) Both (a) and (b)
10. A Ohmmeter is basically:
a) A ammeter
b) A voltmeter
c) A multimeter
d) None of the above
11. A megger indicates infinity when test terminals are open-circuited. This is because:
a) No current flows through the current coil
b) No current flows through the pressure coil
c) No current flows through the compensating winding
d) Current does not flow through current coil and pressure coil
12. Potentiometer is an __ instrument:
a) Indicating
b) Comparison
c) Calibrating
d) Recording
13. Which of the following bridge is frequency sensitive:
a) Wheatstone bridge
b) Maxwell bridge
c) Anderson bridge
d) Wien bridge
14. Tesla coil is a ___ transformer:
a) Coreless
b) Cascaded
c) Low impedance
d) High frequency resonant
15. Direct current is preferred over alternating current for testing of ac transmission lines and cables because:
a) Heavy charging currents will be drawn and so a large sized transformer is required if tested with ac
b) Transmission lines and cables should not be tested with dc
c) The transformers required for testing cannot be used for long distances
d) All the above
1. Moving Iron instruments can be used on:
a) ac and dc both
b) ac only
c) dc only
d) none of the above
2. In spring control instruments, controlling torque:
a) can be adjusted easily
b) cannot be adjusted easily
c) remains the same
d) varies with the load
3. Chemical effect is used for the operation of:
a) voltmeter
b) ammeter
c) ampere hour meter
d) kWh meter
4. The deflection torque can be produced by:
a) gravity control
b) spring control
c) air friction
d) magneitcally
5. Moving coil instruments are:
a) permanent magnet type
b) dynamometer type
c) induction type
d) permanent magnet and dynamometer type
6. For increasing the range of an ammeter, connect:
a) a high value resistance in series with the ammeter coil
b) a high value resistance in parallel with the ammeter coil
c) a low value resistance in parallel with the ammeter coil
d) a low value resistance in series with the ammeter coil
7. A galvanometer can be used for measuring current and voltage of a circuit by:
a) shunt only
b) connecting high value of resistance in series only
c) shunt for measuring current and high resistance in series for voltage
d) without shunt and series resistance
8. Most commonly used watt meter is:
a) induction type
b) electrostatic type
c) dynamometer type
d) moving iron type
9. The energy meter used for measuring energy of a dc circuit is:
a) ampere hour meter
b) induction type
c) electrostatic type
d) dynamometer type
10. The energy consumption of MI instrument as compared to MC instrument is:
a) same
b) more
c) less
d) very small
Power Factor Objective Questions Answers
1. The power factor of ac circuit lies between
a) 0 and 1
b) -1 and 1
c) 0 and -1
d) None of the above
2. A Circuit of zero lagging power factor behaves as:
a) An inductive circuit
b) A capacitive circuit
c) R-L circuit
d) R-C circuit
3. In order to improve the power factor which device should be connected to the power system:
a) Series capacitor
b) Shunt capacitor
c) Series inductor
d) Shunt inductor
4. In an induction motor when the air gap field between rotor and stator increases power factor of the machine:
a) Increases
b) Decreases
c) Does not have any effect
d) None of the above
5. The power factor of an ac circuit is equal to:
a) Cosine of the phase angle
b) Sine of the phase angle
c) Tangent of the phase angle
d) Cotangent of the phase angle
6. In an ac circuit i x sin (Phi) is called the __ component of the current:
a) Watless
b) Reactive
c) Quadrature
d) All the above
7. The heat developed in an electric iron is attributed to __ power
a) Apparent
b) Reactive
c) True
d) True and reactive
8. When the power factor in the transmission line is leading, which device is employed at substation to reduce the power factor:
a) CVT
b) Reactor
c) Synchronous condenser
d) None of the above
9. In a circuit low reactive power compared to true power indicates:
a) Low power factor
b) High power factor
c) Low efficiency
d) High efficiency
10. The rating of given on the name plate of a transformer indicates the:
a) True power which it can supply
b) Apparent power which it can supply
c) Apparent power which it draws from the supply mains
d) True power which it draws from the supply mains
c) A high value of initial capacitance
1. What is The Basic Three Electrical Quantities.
1. Resistance, Capacitance, Inductance
2. Power, Voltage, Conductance
3. Voltage, Current, Resistance(Impedance)
4. Current , Reluctance, Inductance
Answer: 3. Voltage, Current, Resistance (Impedance)
Explanation: The reader may select option 1, but do not forget that there is no concept of Option 1 ( Resistance, Capacitance , inductance ) without Option 3 ( Voltage, Current, Power )
Hence The basic Electrical Quantities are Voltage, Current and Power ( Option 3.
2. In case of Short Circuit,_______Current will flow in the Circuit.
1. Zero.
2. Very Low
3. Normal.
4. Infinite
Answer: 4. Infinite
Explanation: At the short circuited point, the voltage difference is very low (about Zero)
So then put the value in → I = P/V .... so if we put V = 0, Then Current will be infinite.
3. If a 100Watts Bulbs ON for 10 hours, then what will be the amount of consumed Electricity?
1. 100Watts
2. 100Watts per Hour
3. 1000 Watts ( 1kW)
4. 1kWh = 1 Unit of electricity
Answer: 4. 1kWh = 1 Unit of Electricity.
Explanation: The Basic Unit for Consumed Electricity is kWh = one unit (also Called Board of Trade Unit =BTU).
Now, 10 hours x 100 Watts = 1000Watts.Hours = 1kWh.
4. What quantity of charge must be delivered by a battery with a Potential Difference of 110 V to do 660J of Work?
1. 0.6 C
2. 6 C
3. 60 C
4. 600 C
Answer: 2. 6 C.
Explanation:
Q = W / V
= 660 / 110 = 6 C.
5. Ω (Ohm) is the Unit of ___________?
1. Resistance (R)
2. Inductive Reactance ( XL)
3. Capacitive Reactance (Xc)
4. All of the above
5. None of the above
Answer: 4. All of the above
Explanation: As we better know that Inductive and Capacitive reactances are resistances, so the unit of all these quantities should be same i.e Ohm (Ω)
6. Siemens or Mho (℧) is the unit of ____________?
1. Conductance
2. Admittance
3. Both 1 & 2
4. None of the above
Answer: 3. Both 1 & 2.
Explanation: Conductance (G) is the inverse/reciprocal of Resistance (R) and the SI unit of Conductance (G) is Siemens (S) or Mho (℧)
and Admittance (Y) is the inverse/reciprocal of Impedance(Z).
but we also know that impedance(Z) is resistance in AC Circuits. So both of (R) and (Z) are Resistances. Therefore the reciprocal/inverse of R and Z = G and Y respectively. And G and Y are same. So the SI unit of these Quantities ( G and Y ) = Siemens (S) or (or Mho (℧)
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