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Homework Booklet

National 5 Physics

Electricity and Energy Part 2

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DO NOT write on this booklet.

You will be required to return it at the end of the course!

Practice questions on electrical power

(From HSDU Int2 Pupil Materials Pack)

1. a) If an electric current is passed through a conducting wire, what energy transformation takes place?

b) Many electrical appliances in the home are designed to make use of this energy transformation. Name four of these appliances.

2. A light bulb has a power rating of 60 W.

a) What is meant by the term power?

b) How much electrical energy is transformed by the bulb in 1 s?

c) State the energy changes involved when the lamp is switched on.

3. The electric motor on a ceiling fan uses 207 kJ of electrical energy in 30 minutes. a) Calculate the power rating of the motor in the fan.

b) State the energy changes involved when the ceiling fan is switched on.

4. How much electrical energy is used by the following appliances?

a) A 400 W drill used for 45 s

b) A 300 W food processor used for 20 s c) An 800 W iron used for 40 minutes

d) A 2.4 kW kettle that takes 5 minutes to boil the water inside it.

5. What is the power rating of an appliance which transforms - a) 500 J in 5 s

b) 1200 J in 20 s

c) 1.8 MJ in 10 minutes?

6. How long would a 2 kW electric kettle take to boil the water inside if it uses 100 kJ of electrical energy?

7. a) Draw a circuit diagram to show how you would measure the power output of a lamp bulb using a voltmeter and ammeter.

b) If the meter readings were 6 V and 600 mA, what would be the power of the lamp?

c) How much energy would this lamp use in 1 hour?

8. A colour television set is rated at 300 W.

a) Calculate the current drawn by the television when connected to the 230 V mains supply.

b) How much energy would this television use if it was left on overnight for 8 hours?

9. a) Using the equations V = IR and P = VI, show that if a current I flows through a heating element of resistance R, the power of the heater is given by P = I2R.

b) What is power rating of a 30 Ω heating element when 8 A passes through it?

10. Calculate the power rating of the following devices in a car - a) A radio of resistance 6 Ω drawing a current of 2 A.

b) the rear window heater of resistance 3 Ω drawing a current of 4 A.

11. An electric fire is rated at 2 kW, 230 V.

a) What is the current in the heating element when it is switched on?

b) Calculate the resistance of the heating element

12. A 100 Ω resistor has a maximum safe power rating of 4 W. Calculate the maximum current it can safely handle.

13. Calculate the resistance of a hairdryer element which has a power rating of 960 W when drawing a current of 4 A.

14. By combining the equations V = IR and P = VI, show that the power can also be given by P = V2 .

R

15. Calculate the power rating of a heater which has a resistance of 53 Ω working off the mains voltage of 230 V.

16. The fuses used in electrical plugs in the UK come in 2 main sizes - 3 A and 13 A. a) What is the purpose if the fuse in the plug connected to an appliance?

b) Calculate the current drawn by each appliance in the table below.

c) Complete the table below and select which of the above fuses would be most suitable for each of the appliances.

|Appliance |Power |Voltage (V) |Current (A) |Most suitable fuse |

|Food Mixer | |230 |0.3 | |

|Lamp |100 W |230 | | |

|Heater |2.5 kW |230 | | |

|Hi-fi unit | |230 |1.5 | |

d) What is the maximum power rating of appliance that can be used with a 3A fuse?

17. A current of 6 A flows along a flex of total resistance 0.2 Ω to an electric heater which has an element of resistance 60 Ω.

a) Calculate the heat generated each second in i) the flex

ii) the element.

b) Why does the element become hot and the wire remain cool?

c) What size of fuse, 3 A or 13 A, should be fitted to the plug connected to this heater?

Practice questions on Ohm’s Law

(From HSDU Int2 Pupil Materials Pack)

18. In a series circuit, the ammeter reading was noted for different values of resistor in the circuit.

a) Which electrical quantity does the ammeter measure?

b) Copy and complete the table below, placing the ammeter readings in the correct order.

0.6 A, 2.4 mA, 1.2 A, 240 mA.

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19. The current in a lamp bulb was 2 A when connected to a 12 V battery. Calculate the resistance of the lamp bulb.

20. When connected across a 3 V supply, the current in a resistor was 60 mA. What is the value of the resistor?

21. A 220 Ω resistor is connected across a 2 V supply. What is the current in the resistor?

22. A 12 V transformer is connected to a circuit of resistance 1.2 kΩ. What is the current in the circuit?

23. Calculate the missing quantities in the circuits below.

24. The diagram below shows a 6 V 60 mA lamp working off a 24 V supply.

a) What must be the potential difference across the resistor if the lamp is operating correctly?

b) Calculate the value of the resistance of resistor R.

25. Potential difference and current were measured in both circuits below for different

values of current

The results for each circuit are shown below:

a) Copy and complete both tables.

b) What happens to the voltage across the lamp as the current in the circuit increases

c) What conclusion can be drawn about the resistance of the lamp bulb as the current increases?

d) What conclusion can be drawn about the resistance of the resistor as the current increases?

e) Explain the difference in the behaviour of the lamp bulb and the resistor as the current increases.

f) Plot a graph of voltage and current for the bulb and use the graph to:

i) estimate the current through the bulb when the voltage across the bulb is 3.3V

ii) predict the current through the bulb when the voltage across the bulb is 5.0V

Practice questions on resistors in series and parallel

(From HSDU Int2 Pupil Materials Pack)

26. Calculate the total resistance between X and Y for the following.

[pic]

27. Calculate the total resistance between X and Y for the following circuits.

[pic]

28. a) What will be the resistance of ten 20 Ω resistors when they are connected in series?

b) What will be the resistance of ten 20 Ω resistors when they are connected in parallel?

29. You are given the four resistors below.

1 Ω, 10 Ω, 100 Ω, 1000 Ω

a) What is their total resistance when they are connected in series?

A less than 1 Ω

B between 1 Ω and 10 Ω

C between 10 Ω and 100 Ω

D between 100 Ω and 1000 Ω

E greater than 1000 Ω

b) What is their total resistance when they are connected in parallel?

A less than 1 Ω

B between 1 Ω and 10 Ω

C between 10 Ω and 100 Ω

D between 100 Ω and 1000 Ω

E greater than 1000 Ω

Practice questions on complex circuits

(From HSDU Int2 Pupil Materials Pack)

30. Calculate the resistance between X and Y in the following resistor networks.

[pic]

c) Calculate the current drawn by circuit (a) when it is connected to a 6V supply.

31. The following potential divider circuit was set up using the values shown.

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a) Calculate the current in the circuit through R1 and R2.

b) Calculate the value of the potential differences (voltages) V1 and V2, across each resistor.

c) Use your results to show that the relationship [pic] is true.

d) Use your results to show that the relationship [pic] is also true, where

VS = supply voltage.

32. Calculate the value of V1 in the following circuits.

a)

6 kΩ 3 V

12 kΩ V1

b)

4 kΩ

500 Ω

24 V

V1

33. Calculate the value of V1 in the following circuits.

a)

12 V

15 kΩ

10 kΩ V1

b)

20 V

250 Ω

5 kΩ V1

34. A fixed 6 V d.c. power supply has to be reduced to give constant output of 1.5 V using a potential divider.

Design a potential divider circuit that will give a constant output of 1.5 V from the 6 V

supply.

35. A 20 kΩ potentiometer AB is connected across a 6V d.c. power supply as shown below.

B

+

6 V 20 kΩ P

- V1

A

The sliding contact, P, can be moved to any point along the potentiometer AB.

a) What will be the output voltage, V1, when the sliding contact, P, is at i) position A

ii) position B

iii) midway between A and B?

b) What would be the output voltage, V1, if the sliding contact P was one third of the length along the potentiometer from A?

c) What would be the resistance between points A and P if the potentiometer was adjusted to give an output voltage of 3.5V?

36. Why must a resistor be connected in series with a light emitting diode when using a 5 V

supply?

37. An LED and resistor are connected in series to a 5 V supply as shown. The maximum allowed current through the LED is 12 mA. The voltages are given.

A

3 V

2 V

B

a) +5 V and 0 V are to be connected to the circuit. Which will be connected to A and

B if the LED is to light?

b) What is the maximum current through the resistor.

c) What is the value of the resistor needed to protect the LED?

38. An LED is connected as shown and the following data for the LED is shown.

Vs = 3 V

Imax = 20 mA

R Vmax = 1 V

Calculate the least value of resistance of the resistor R, placed in series with the LED, which would allow it to work properly.

39. Calculate the following protective resistors from the following data. a) Vs = 6 V LED (Vmax = 1.5 V Imax = 50 mA).

b) Vs = 10 V LED (Vmax = 2.0 V Imax = 100 mA).

c) Vs = 5 V LED (Vmax = 1.5 V Imax = 50 mA).

40. State what happens to the resistance of:

a) a thermistor subjected to increasing temperature

b) an LDR as the light intensity falling on it increases.

41. a) A thermistor is connected in series to a resistor is connected to a 5 V supply as

shown. What will happen to the output voltage as the temperature of the thermistor rises?

b) What difference would there be to the output voltage

if the thermistor and the 4 kΩ resistor were interchanged?

+5 V

0 V

4 kΩ

Vout

42. Calculate the current and voltage reading in the following circuits.

a) b) c)

A A

2 kΩ

6 V

0 V

4 kΩ

2 kΩ

5 V

0 V

V 8 kΩ

V

10 V

0 V

6 kΩ

4 kΩ V

A A A

d) e) f)

15 V

0 V

7 kΩ

5 kΩ

V

12 V

0 V

2 kΩ

1 kΩ

3 kΩ

5 V

0 V

V 7 kΩ V

43. An LDR is connected to a 5 kΩ resistor as shown.

The values of its resistance for particular conditions are shown below.

+5 V

5 kΩ Vout

0 V

What will be the output voltage when the LDR is

a) in the dark b) in sunlight?

44. The circuit below shows a temperature sensing device.

5 V

1 kΩ

a) Calculate the voltage across the base-emitter of the transistor:

i) in the cold when the resistance of the thermistor is 9 kΩ.

ii) at 100 °C when its resistance is 1 kΩ.

b) Hence explain how the circuit works.

c) How could you alter the sensitivity of the device?

45. Design a circuit which would allow an LED to light when it gets too dark.

Open Ended Questions for Electricity

46. LEDs and filament lamps are examples of output devices. Use your knowledge of physics to explain why LEDs are replacing filament lamps.

47. Draw a circuit diagram using at least three different components from the following list and explain the operation of the circuit.

cell, battery, lamp, switch, resistor, variable resistor, voltmeter, ammeter, LED, motor, microphone, loudspeaker, photovoltaic cell, fuse, diode, capacitor, thermistor, LDR, relay, transistor.

48. A pupil comments that this component is called a resistor because it slows down the flow of charge.

[pic]

Using your knowledge of physics comment on this statement.

49. Students in a National 5 physics class are evaluating each other circuit designs. One student comments that one of the circuits could be improved by use of a bigger resistor. Using your understanding of Physics comment on the use of the phrase “bigger” resistor.

50. A national 5 student comments that when using ammeters and voltmeters, ammeters are easier to use as they can be placed anywhere in a circuit but care must be taken with the location of voltmeters.

Comment on this statement using your knowledge of physics.

51. Using your knowledge of physics explain why a light bulb does not always obey Ohm’s Law.

52. Discuss why Ohm’s Law is not appropriate for a thermistor.

53. Using your knowledge of physics discuss the difference between power, current and voltage.

National 5 Section 1 Exam Style Questions for Electricity

54. (Int 2 Past Paper)

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55. (Int 2 Past Paper)

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56. (Int 2 Past Paper)

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57. (Int 2 Past Paper)

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58. (Int 2 Past Paper)

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59. (Int 2 Past Paper)

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60. (Int 2 Past Paper)

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61. (Int 2 Past Paper)

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62. (Int 2 Past Paper)

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63. (Int 2 Past Paper)

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64. (Int 2 Past Paper)

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65. (Int 2 Past Paper)

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66. (Int 2 Past Paper)

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67. (Int 2 Past Paper)

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68. (Int 2 Past Paper)

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69. (Int 2 Past Paper)

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70. (Int 2 Past Paper)

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71. (Int 2 Past Paper)

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72. (Int 2 Past Paper)

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73. Int2 2007 qn 8

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74. Int2 2007 qn9

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75. Int2 2007 qn13

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76. Int2 2007 qn 14

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77. Int2 2008 qn8

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78. Int2 2008 qn9

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79.Int2 2008 qn10

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80.Int2 2008qn11

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81.Int2 2009 qn9

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82.Int2 2009 qn10

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83.Int2 2009 qn11

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84.Int2 2010 qn7

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85.Int2 2010 qn8

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86.Int2 2010 qn9

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87.Int2 2011 qn6

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88.Int2 2011 qn7

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89.Int2 2012 qn13

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90.Int2 2012 qn14

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National 5 Section 2 Exam Style Questions for Electricity

91. (Int 2 Past Paper)

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92. (Int 2 Past Paper)

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93. (Int 2 Past Paper)

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94. (Int 2 Past Paper)

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95. (Qn 5 Credit Physics 2007)

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96. (Qn 4 Credit Physics 2008)

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97. (Qn 3 Credit Physics 2010)

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98. (Qn 3 Credit Physics 2011)

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99. (Qn 3 Credit Physics 2012)

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100.Int2 2012 qn 24

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101.Int2 2012 qn 25

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102.Int2 2011 qn25

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103.Int2 2011 qn27

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104.Int2 2010 qn24

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105.Int2 2010 qn26

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106.Int2 2009 qn25

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107.Int2 2008 qn25

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108.Int2 2008 qn27

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Practice questions on electrical power

(From HSDU Int2 Pupil Materials Pack)

1. a) energy is transferred to the appliance through electricity and is transferred from the appliance through heating

b) Iron, kettle, toaster, hair-straightners, etc.

2 a) Energy per unit time

b) 60J

c) energy is transferred to the bulb by electricity and from the bulb through heating and light

3. The electric motor on a ceiling fan uses 207 kJ of electrical energy in 30 minutes. a) 115W

b) energy is transferred to the fan by electricity and is stored in the fan kinetically

4. How much electrical energy is used by the following appliances?

a) 18,000J

b) 6,000J

c) 1.920,000J

d) 720,000J

5. What is the power rating of an appliance which transforms - a) 100W

b) 60W

c) 3000W

6. 50s

7. a) Ammeter in series and voltmeter in parallel

b) 3.6W

c) 12,960J

8. A colour television set is rated at 300 W.

a) 1.3A

b) 144,000W

9. a) starting with P = VI, substitute V=IR, then P=IRI= I2R.

b) 1920W

10. Calculate the power rating of the following devices in a car - a) 24W

b) 48W

11. An electric fire is rated at 2 kW, 230 V.

a) 8.7A

b) 26Ω

12. 0.2A

13. 60Ω

14. starting with P = VI, substitute I=V/R to get P = V x V/R = P = V2 .

R

15. 998W

16. a) To protect the flex

b) and c)

|Appliance |Power |Voltage (V) |Current (A) |Most suitable fuse |

|Food Mixer | |230 |0.3 | |

|Lamp |100 W |230 |0.4 |3A |

|Heater |2.5 kW |230 |10.8 |13A |

|Hi-fi unit | |230 |1.5 | |

d) 690W

17. a) i) 7.2J

ii) 2160J

b) The higher resistance means more energy is dissipated by the resistor.

c) 13A

Practice questions on Ohm’s Law

(From HSDU Int2 Pupil Materials Pack)

18. a) Current

b) 1.2 A, 0.6 A, 240 mA, 2.4 mA

19. 6Ω

20. 50Ω

21. 9mA

22. 0.01A

23. a) 75Ω b)18mA c) 75V d) 100Ω

24. a) 18V

b) 300Ω

25. a) 1st table: 10.0, 10.3, 10.6, 12 2nd table: 10.0, 10.0, 10.0, 10.0

b) Increases

c) As the current increases the resistance of the bulb increases

d) The current does not affect the resistance of the resistor

e) The resistor is an ohmic device but the bulb in non-ohmic because it heats up as the current flows through it.

f) i) 0.32A ii) 0.44A

Practice questions on resistors in series and parallel

(From HSDU Int2 Pupil Materials Pack)

26. a) 16Ω b) 2.0kΩ c) 1.6kΩ

27. a) 2Ω b) 3Ω c) 9Ω d) 4Ω e) 3.6Ω f) 6.8Ω

28. a) 200Ω b) 2Ω

29. a) E greater than 1000 Ω b) A less than 1 Ω

Practice questions on complex circuits

(From HSDU Int2 Pupil Materials Pack)

30. a) 45Ω b) 33Ω c) 0.13A

31. a) 0.5mA

b) V1 = 4V and V2 = 6V

32. a) 6V b) 3V

33. a) 4.8V b) 19V

34. Any combination of resistors in series in a 1:3 ratio.

35. a) i) 0V ii) 6V iii) 3V

b) 2V

c) 11.7kΩ

36. To reduce the current in the circuit to protect the LED

37. a) A = +5V and B = 0V

b) 12mA

c) 250Ω

38. 100Ω

39. a) 90Ω b) 80Ω c) 70Ω

40. a) decreases

b) decreases

41. a) decreases b) increase instead

42. a) 1mA, 4V b) 0.5mA, 1V c) 1mA, 4V d) 1.25mA, 8.75V e) 4mA, 4V

f) 0.5mA, 3.5V

43. a) 1V b) 0.2V

44. a) i) 0.5V

ii) 2.5V

b) As temperature increases the resistance of the thermistor decreases. As the resistance of the thermistor decreases the voltage across the thermistor decreases. Since the thermistor and resistor are in series as the voltage across the thermistor decreases the voltage across the resistor increases. The voltage across the resistor is connected to the transistor. As the voltage across the resistor increases the transistor turns on.

c) Reduce the resistance of the resistor.

45. Ask your teacher to check your design.

National 5 Section 1 Exam Style Questions for Electricity

54. . (Int 2 Past Paper) A

55. (Int 2 Past Paper) D

56. (Int 2 Past Paper) C

57. (Int 2 Past Paper) B

58. (Int 2 Past Paper) E

59. (Int 2 Past Paper) C

60. (Int 2 Past Paper) C

61. (Int 2 Past Paper) B

62. (Int 2 Past Paper) D

63. (Int 2 Past Paper) B

64. (Int 2 Past Paper) D

65. (Int 2 Past Paper) C

66. (Int 2 Past Paper) E

67. (Int 2 Past Paper) A

68. (Int 2 Past Paper) B

69. (Int 2 Past Paper) C

70. (Int 2 Past Paper) A

71. (Int 2 Past Paper) A

72. (Int 2 Past Paper) E

73. Int2 2007 qn 8 D

74. Int2 2007 qn9 B

75. Int2 2007 qn13 B

76. Int2 2007 qn 14 A

77. Int2 2008 qn8 D

78. Int2 2008 qn9 C

79. Int2 2008 qn10 D

80. Int2 2008qn11CD

81. Int2 2009 qn9 B

82. Int2 2009 qn10 E

83. Int2 2009 qn11 B

84. Int2 2010 qn7 E

85. Int2 2010 qn8 C

86. Int2 2010 qn9 D

87. Int2 2011 qn6 B

88. Int2 2011 qn7 A

89. Int2 2012 qn13 B

90. Int2 2012 qn14 D

National 5 Section 2 Exam Style Questions for Electricity

91. (Int 2 Past Paper)

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92. (Int 2 Past Paper)

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[pic]No force

[pic] Force

As force increases, resistance increases.

c) [pic] [pic]

93. (Int 2 Past Paper)

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94. (Int 2 Past Paper)

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95. (Qn 5 Credit Physics 2007)

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96. (Qn 4 Credit Physics 2008)

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97. (Qn 3 Credit Physics 2010)

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98. (Qn 3 Credit Physics 2011)

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99. (Qn 3 Credit Physics 2012)

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100.Int2 2012 qn 24

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101.Int2 2012 qn 25

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102.Int2 2011 qn25

a) [pic]

b)

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c) [pic]

103.Int2 2011 qn27

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104.Int2 2010 qn24

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105.Int2 2010 qn26

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106.Int2 2009 qn25

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107.Int2 2008 qn25

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108.Int2 2008 qn27

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-----------------------

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