QUESTION 1



Grade 12

PHYSICAL SCIENCES

EXAM PAPER 1

Time: 3 hours Marks: 150

INSTRUCTIONS AND INFORMATION

Read the following carefully before answering the questions that follow:

1. Answer ALL the questions.

2. Number the questions exactly as the questions are numbered.

3. Start the answer to each question at the top of a new page.

4. All sketches are to be done in pencil and labelled in ink.

5. Write neatly and legibly.

6. Non-programmable calculators can be used.

7. The diagrams in the question paper are not necessarily drawn to scale.

SECTION A

QUESTION 1

There are four possible options for each answer in the following questions. Each question has only ONE correct answer. Choose the correct answer and write only A, B, C or D next to the question number.

1.1 Astronomers analyse the spectrum of light from a star. They have found that the light from other galaxies moving away from us has a red shift. Which of the following statements are FALSE?

A Light shifts to red since red has the lowest frequency of visible light.

B Light shifts to red since red has the longest wavelength of visible light.

C Red shift is due to the Doppler Effect of electromagnetic waves.

D The red shift implies that galaxies are receding slowly and that the universe is getting smaller. (2)

1.2 A current-carrying conductor is placed in a magnetic field. The current flows into the page.

[pic]

In which direction will the conductor experience a force?

A 1

B 2

C 3

D 4 (2)

1.3 In a 1 000 W hairdryer connected to a 220 V line in South Africa, most of the current goes through the heating coils, a pure resistance. Which row of the table correctly shows the resistance and the maximum current in the hairdryer?

| |Maximum current |Resistance |

|A |[pic] |[pic] |

|B |[pic] |[pic] |

|C |[pic] |[pic] |

|D |[pic] |[pic] |

(2)

1.4 Which electromagnetic wave in column X matches the everyday context described in column Y?

| |Column X |Column Y |

|A |Microwaves |Can pass through metals |

|B |Gamma rays |Is diffracted round hills |

|C |Infrared |Can cause sunburn |

|D |Visible light |Used in lasers |

(2)

1.5 When a cathode of a photoelectric cell is illuminated with blue light of frequency f, the electrons emitted have a maximum kinetic energy of Ek. For which one of the following graphs is the relationship between Ek and f best illustrated for the photocell?

[pic] (2)

1.6 You can replace two forces, P and Q, with a single force of 7 N. If the magnitude of force P is 3 N, which one of the following can be the magnitude of force Q?

A 2 N

B 3 N

C 8 N

D 13 N (2)

1.7 You push the south pole of a bar magnet into end X of a long solenoid. The ammeter that is connected to the solenoid shows a deflection to the left.

[pic]

Which additional movement of the bar magnet will produce the same deflection on the ammeter?

A pushing the north pole of the magnet into end Y of the solenoid

B pulling the north pole of the magnet out of end X of the solenoid

C pulling the south pole of the magnet out of end Y of the solenoid

D pushing the south pole of the magnet into end Y of the solenoid (2)

1.8 A step-down transformer changes 240 V AC to 6 V AC. There are 75 turns on the secondary coil. How many turns are there on the primary coil?

A 40

B 75

C 240

D 3 000 (2)

1.9 The following diagram shows a beam of electrons entering a magnetic field.

[pic]

In which direction will the electrons be deflected?

A out of the plane of the diagram

B into the plane of the diagram

C towards the top of the diagram

D towards the bottom of the diagram (2)

1.10 Which of the following statements is true for a parallel plate capacitor?

A The unit of capacitance is always given as nanoFarad (nF).

B A 50 nF parallel plate capacitor can only store 50 C of charge.

C The capacitance is dependent on the area of the plates.

D The potential difference applied to the capacitor is inversely proportional to the amount of charge stored. (2)

[20]

QUESTION 2

Complete the following statements by filling in the missing word or phrase.

2.1 An observer walks past two loudspeakers that are 2 m apart. The observer notices that there are places where the sound is louder and where the sound is almost inaudible. This is due to __________ of waves. (1)

2.2 The component needed to ensure continuous rotation in the DC electric motor is the ____________________. (1)

2.3 Microwaves, rather than radio waves with a longer wavelength, are used for satellite communication. This is to minimise the effects of ____________. (1)

2.4 An electric toaster uses _____________ light, a component of the electromagnetic spectrum, to toast bread. (1)

2.5 The product of a net force and the time interval over which the net force acts (1)

[5]

TOTAL FOR SECTION A - 25 marks

SECTION B

QUESTION 3

Study the following diagram and answer the questions below.

[pic]

3.1 If the frequency of ultrasound used by a sonar system is 40 kHz, what is the wavelength of ultrasound if the speed of sound in water is 1 500 m.s–1? (4)

3.2 If there is a time of 0,1 s between a pulse being sent and received, what is the depth of the water below the boat? (4)

3.3 What time would be recorded by the sonar receiver if the boat was above a shoal of fish

10 m below the surface? (4)

3.4 The speed of ultrasound in air is about 350 m.s–1. Why does ultrasound travel much faster in water than it does in air? (4)

[16]

QUESTION 4

A sodium lamp used in the laboratory during a practical produces yellow light with a wavelength of 6,0 x 10–7 m. A group of students conducting the practical calculated that the energy of a photon of the light is 3,3 x 10–19 J.

4.1 Is their calculation of the energy of the photon accurate? Substantiate your answer with your own calculation. (6)

The sodium lamp is marked 330 W.

4.2 What does this marking mean? (2)

4.3 Only one-fifth of the energy supplied to the light is converted to yellow light. Calculate the number of photons emitted per second by the lamp. (6)

The group of students design a cost-effective way of demonstrating the photoelectric effect. They propose that a 40 W light bulb, a 100 W light bulb and an ultraviolet lamp held in turn at the same distance above a zinc metal sheet placed on a negatively charged electroscope has a significant visual impact in illustrating the emission of electrons.

[pic]

4.4 It was found that the electroscope leaves collapse only when the ultraviolet light was held above the electroscope. Explain this phenomenon. (3)

4.5 Would the deflection of the electroscope be affected if the 100 W bulb was held closer to the zinc metal sheet? Give a reason for your answer. (2)

4.6 What effect would an operating radio held above the electroscope, at the same height as the light in 4.4, have? (1)

4.7 Give a reason for your answer in 4.6. (2)

[22]

QUESTION 5

A metal-coated cathode of a photocell is illuminated first with green light and then with yellow light. Electrons are emitted from the metal surface when green light is used, but not when yellow light is used.

[pic]

Josh suggests that red light, like green light, will also result in electrons being emitted from the cathode.

5.1 Do you agree with Josh’s suggestion? Give reasons for your answer. (4)

5.2 What would the effect on the cathode of the photocell be if it were irradiated with blue light? Give a reason for your answer. (3)

It requires 3,118 x 10–19 J of energy to remove a single electron form the surface of the cathode when the metal is illuminated with light having a wavelength of 0,6 μm in air.

5.3 Determine the energy of the photon. (6)

5.4 What will the energy of the electron be? (3)

5.5 Determine the speed with which the electron is ejected. (4)

[20]

QUESTION 6

A compressed spring joins two trolleys with masses of 2 kg and 3 kg. The trolleys move at a velocity of 1,5 m(s–1 to the left under frictionless conditions on a horizontal surface.

[pic]

6.1 State the law of conservation of linear momentum in words. (3)

The compressed spring between the trolleys is released. Immediately after the spring expands fully, the velocity of the 3 kg trolley is 0,5 m(s–1 to the right.

6.2 Say whether the total momentum of the system changes. (1)

6.3 Calculate the velocity of the 2 kg trolley after the spring expands. (6)

[10]

QUESTION 7

Zayn sets up the following circuit. He uses a battery with an emf of 12 V. The internal resistance of the battery is so small that he can ignore its effects. His circuit contains four resistors, an ammeter and a switch. The diagram shows the values of the resistors. He then closes the switch, S.

[pic]

7.1 Calculate the total resistance of the circuit. (4)

7.2 Calculate the reading on the ammeter. (4)

7.3 He then connects a voltmeter across various points in the circuit. Calculate the reading he gets on the voltmeter when he connects it across the following points.

a) P and Q (2)

b) W and X (2)

[12]

QUESTION 8

A small point charge carries a charge of +4 ( 10–10 C.

[pic]

8.1 Calculate the magnitude of the electric field strength at a distance of 30 mm from the point charge. (4)

8.2 A second point charge of –8 ( 10–10 C is placed at position X. Calculate the magnitude of the force between the charges. (4)

8.3 Identify whether this is a force of attraction or repulsion. (1)

[9]

QUESTION 9

The siren of a police car produces a sound of frequency 420 Hz. A man sitting next to the road notices that the pitch of the sound changes as the car moves towards and then away from him.

9.1 Write down the name of the above phenomenon (1)

9.2 Assume that the speed of sound in air is 340 m∙s-1. Calculate the frequency of the sound of the siren observed by the man, when the car is moving towards him at a speed of 16 m∙s-1. (4)

9.3 The police car moves away from the man at constant velocity, then slows down and finally comes to rest.

9.3.1 How will the observed frequency compare with the original frequency of the siren when the police car moves away from the man at a constant velocity? Write only GREATER THAN, SMALLER THAN or EQUAL TO. (2)

9.3.2 How will the observed frequency change as the car slows down whilst moving away? Write down only INCREASES, DECREASES or REMAINS THE SAME. (2)

[9]

QUESTION 10

Lights in SA households are connected in parallel. Two light bulbs, rated at 100 W; 220 V and 60 W; 220 V respectively, and are connected to an AC source of rms value 220 V. A fuse is connected in series with the bulbs and can allow a current of 10 A.

10.1 Draw the circuit. (3)

10.2 Calculate the peak voltage of the source. (3)

10.3 Calculate the resistance of the 100 W light bulb, when operating at optimal conditions. (3)

10.4 An electric iron, with a power rating of 2 200 W, is now connected across the 60 W globe.

Explain, with the aid of a calculation, why this is not advisable (5) [14]

QUESTION 11

During an experiment to determine the work function of a certain metal, light of different frequencies was shone on the metal surface and the corresponding kinetic energies of the photoelectrons were recorded as shown in the table below.

|Frequency of incident light (x 1014 Hz) |Kinetic energy of photoelectrons (x 10-19 J) |

|6,6 |0,7 |

|8,2 |1,6 |

|9,2 |2,2 |

|10,6 |3,0 |

|12 |3,8 |

11.1 Define the term work function. (2)

11.2 Use the data in the table above to draw a graph of kinetic energy versus frequency on the graph paper provided. (6)

11.3 Extrapolate your graph to cut the X-axis.

11.3.1 What is the frequency at the point of intercept? (2)

11.3.2 What term is used to describe this frequency? (1)

11.4 Use your graph to determine the work function of the metal. (3) [14]

TOTAL FOR SECTION B - 125 marks

[TOTAL: 150 marks]

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