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

Various possible answers are provided for each question. Write the letter only of the correct answer next to the corresponding number.

1.1 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)

1.2 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)

1.3 Town X is 1 500 km east of town Y. On a windless day, a plane flying from town X at a constant velocity of 500 km.h–1, reaches town Y in 3 hours. On another trip, the plane, after having flown for 90 minutes (1[pic] hrs) at 500 km.h–1, suddenly experiences a northerly wind (that is, a wind blowing from the north).

[pic]

If the plane is still to reach town Y in the prescribed time (3 hrs), what changes, if any, should the pilot make to the magnitude and direction of the flight velocity (air speed) of the plane?

| |Magnitude of flight velocity (km.h–1) |Direction of flight velocity |

|A |remain constant at 500 |no change |

|B |remain constant at 500 |north of east |

|C |increase to greater than 500 |north of east |

|D |increase to greater than 500 |south of east |

(2)

1.4 Eagles can tuck in their wings and free-fall straight down when diving for fish. In the instance graphically described, the eagle starts its dive from a height where its vertical velocity is zero. Suppose that when the eagle starts its dive, it cannot change its path once committed. For which one of the following graphs will the velocity reached by the eagle in a time t, be given by the area underneath the graph?

[pic] (2)

1.5 Two forces, each of magnitude 200 N, are simultaneously applied to a stationary crate at rest on a smooth horizontal surface as shown in the diagram below.

[pic]

Work will be done on the crate because the crate will …

A be lifted off the surface.

B move to the left.

C move to the right.

D remain at rest. (2)

1.6 A plane is travelling at 900 m.s–1 in the air where the speed of sound is 300 m.s–1. A shock wave is formed. Which one of the following statements regarding the shock wave formed is correct? The shock wave formed is due to ...

A constructive interference of a large number of wave-fronts directly behind the plane.

B constructive interference of a large number of wave-fronts directly in front of the plane.

C destructive interference of a large number of wave-fronts directly behind the plane.

D destructive interference of a large number of wave-fronts directly in front of the plane. (2)

1.7 A cartoon is drawn on a sheet of white paper using red ink. The cartoon is then looked at through a red filter and a green filter at the same time.

[pic]

The cartoon is indistinguishable to the eye because …

A white light is reflected to the eye.

B all the light is absorbed and none is reflected to the eye.

C only red light is reflected to the eye.

D yellow light reflected to the eye is hard to see. (2)

1.8 In a colour TV there are three electron guns: a red gun, a blue gun and a green gun. The red gun receives the red signal from the TV station, while the blue gun receives the blue signal and the green gun receives the green signal. If you look closely at a TV screen, you will see it is covered with groups of red, green and blue dots.

[pic]

Which of the following statements best describes the reason for the TV screen comprising red, green and blue dots?

A Red, blue and green are primary colours that together form white light.

B The beam from the red gun can form black when it strikes the green and blue dots.

C Red, blue and green are secondary colours that can produce a complete range of colours when mixed in varying amounts.

D Red, blue and green are primary colours that can produce a complete range of colours when mixed in varying amounts. (2)

1.9 Which one of the following indicates that light is an electromagnetic wave?

A Undergoes interference.

B Travels at 3 x 108 m.s–1 in a vacuum.

C Can be polarised.

D Can be reflected. (2)

1.10 Anda, a passenger train commuter, stands in the coach of a passenger train moving at a high constant speed on the straight section of a line between two stations. A ball is dropped and comes rolling towards him. He jumps straight upwards to avoid the ball and lands on his feet again. The position on the coach floor where he lands will probably be ... from where he jumped.

A the same position

B slightly forward

C slightly backward

D a noticeable distance backward (2)

[20]

QUESTION 2

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

2.1 A moving coil microphone does not need a battery or a power supply. The energy needed to cause movement comes from _______________. (1)

2.2 An object of mass M is at rest at position A as shown.

[pic]

It rolls down an inclined plane. If the momentum of the object doubles as it speeds up, the kinetic energy is increased ________________ times. (1)

2.3 The physical quantity equal to the rate of change in momentum is _____________. (1)

2.4 When one looks into a pool of water, the image of an object under the water is a ______________ image. (1)

2.5 Photoelectric emission demonstrates that light has a ____________ nature. (1)

[5]

TOTAL FOR SECTION A - 25 marks

SECTION B

QUESTION 3

A bicycle lamp is actually a dynamo, i.e. a simple application of a generator. As the bicycle speeds up, the magnet rotates faster.

3.1 What impact does the increase in speed of the bicycle have on the dynamo? Your answer must refer to two changes that take place. (2)

Electricity can be generated using a system similar to that used in the bicycle lamp, where wind or water is the resource used to turn large turbines.

3.2 Can you think of ONE advantage and TWO disadvantages of generating electricity from wind power? (3)

3.3 South Africa can generate some of its electricity from nuclear power at the Koeberg Power Plant. Outline some advantages and the disadvantages of generating electricity from nuclear power. (4)

The following extract is from an article about wind-driven electricity generators:

|Scientists have found a way to iron out what are described as bumps in the wind. |

| |

|These so-called bumps are caused by the ever-changing strength of the wind. It can change speed every 5 to 20 seconds and when |

|it is being tapped by wind machines, this can play on-off havoc with a diesel generator back-up, causing high fuel consumption |

|and engine wear. |

| |

|(The Guardian, 6/9/88) |

3.4 Suggest why a wind turbine generator is particularly suitable in the mountainous town of Darling in the Western Cape. (1)

3.5 Why is a diesel generator as well as a wind turbine recommended? (2)

3.6 What does the phrase “on-off havoc with a diesel generator” mean? (2)

3.7 Why can this cause high fuel consumption and engine wear? (1)

[15]

QUESTION 4

A parachutist is descending towards the ground at a constant velocity of 6,5 m.s–1. At a height of 300 m above the ground, he throws a glass marble with a mass of 40 g vertically upwards at 1,5 m.s–1.

4.1 Calculate the velocity at which the marble was thrown relative to the ground. (2)

4.2 Calculate the velocity with which the marble strikes the ground if air friction is ignored. (4)

4.3 In fact, air resistance plays a significant role. If the marble strikes the ground with a velocity of 60 m.s–1, calculate the work done in overcoming air friction. (5)

4.4 Explain in which of the above cases, with or without air friction, mechanical energy is not conserved. (4)

[15]

QUESTION 5

Read the following passage and then answer the questions below.

|South Africa does not have a supply of oil. As a result, the SASOL process was developed, which uses technology to make petrol|

|from coal. This process makes large sums of money for the government. They used a cheap labour force to produce the petrol, |

|and, even though the petrol was made in South Africa, it was not any cheaper than petrol imported from other countries. The |

|SASOL process has also damaged the environment by polluting the air with poisonous gases. People who live or work in |

|Sasolburg, where the first SASOL factory was constructed, say that it is very smelly and dirty because of the pollution. |

| |

|In the 1980’s an attempt was made by the South African government to extract natural gas and oil from the sea. This was called|

|the MOSSGAS project, because the natural gas was found off the South Coast near Mossel Bay. This project cost the South |

|African public billions of rands in taxes. However, the project was a failure because there was not enough oil and gas to make|

|it worthwhile to mine. |

| |

|By Chris Waverly in Learning about Technology, published by Uswe, 1996 |

5.1 With the hindsight given by this article, do you think that it was wise for South Africa to engage in projects like SASOL and MOSSGAS? Present your answers in terms of advantages and disadvantages. (4)

5.2 How could the problem of pollution by SASOL be reduced to a safe level? (3)

5.3 While projects like SASOL and MOSSGAS use available, non-renewable natural resources, their use is not ideal in terms of the well-being of the planet. Why is this the case? (3)

5.4 What viable, renewable energy resources do you think should be major considerations in planning for South Africa’s future? (2)

[12]

QUESTION 6

The information in the table below was obtained from a students’ practical sheet.

| | |Sound |Light |

|a |Transverse wave |No |Yes |

|b |Longitudinal wave |Yes |No |

|c |Diffraction |Yes |Yes |

|d |Refraction |Yes |Yes |

|e |Interference |No |Yes |

|f |Frequency |? |? |

6.1 Which of the tabulated results in either a, b, c, d or e is/are correct? Give a reason for your answer. (3)

6.2 Which of the tabulated results in either a, b, c, d or e is/are incorrect? Give a reason for your answer. (3)

6.3 How do the frequencies for sound and light differ? (2)

6.4 Do the varying frequencies of light and sound impact on their respective wavelengths? Explain. (2)

6.5 Will using red light and blue light impact on interference patterns obtained? You may use sketches in your explanation. (4)

[14]

QUESTION 7

Consider a police car, siren blaring, moving from rest towards the right. Both observers are on the sidewalk (pavement).

[pic]

7.1 When the police car is stationary, describe the sound heard by each observer. (2)

7.2 As the police car moves between the two observers, describe the sound heard by each observer. (2)

7.3 What is the name given to the phenomena described in 7.1 and 7.2? (2)

The siren of the police car at rest emits a dominant frequency of 1 600 Hz.

7.4 What frequency will you hear if you are at rest and the police car moves towards you at 25 m.s–1 ? (4)

[10]

QUESTION 8

Consider an extract from the following press release by Public Enterprises Minister Alec Erwin.

|Nuclear power is best for the future – Erwin |

| |

|The Pebble Bed Modular Reactor (PBMR) offers an efficient and economical method of providing power to South Africa’s coastal |

|towns and cities, Public Enterprises Minister Alec Erwin said. |

| |

|“Given the urgent demand for large-scale, clean, affordable energy – and South Africa’s lack of primary fuel sources at its |

|coastal regions – the PBMR provides a plausible and cost-competitive alternative solution” said Erwin. |

| |

|Other possibilities were the construction of very long and expensive power lines, or setting up the logistics to supply |

|conventional coastal power stations with natural gas or coal. |

| |

|“Both of these solutions are expensive”, said Erwin. |

| |

|PBMRs could be located close to the point of use, and there was no need to upgrade either transmission or rail structure, |

|Erwin explained. |

| |

|PBMRs are small, high-temperature nuclear reactors. The “pebbles” referred to are the fuel – enriched uranium dioxide encased |

|in a graphite sphere about the size of a billiard ball. |

| |

|Each module produces 400 MW, and two of them could be fitted into an area the size of a soccer field. The modular design |

|allows for additional units to be added, according to demand. |

| |

|Cape Times, June 06, 2006 |

8.1 Discuss Minister Erwin’s reference to “the urgent demand for large-scale, clean, affordable energy”. (4)

8.2 Briefly explain the way in which the PBMR harnesses energy from enriched uranium. Use a simple sketch in your answer. (3)

8.3 Do you think an increase in nuclear power is the best way to solve South Africa’s increasing energy demands? (3)

8.4 South African environmental group Earthlife Africa has warned of a possible nuclear disaster if the government does not consider alternative energy sources to the proposed PBMR. Discuss potential disasters that may occur. (4)

[14]

QUESTION 9

The battery in the circuit below has an emf of 12 V and an internal resistance of 0,2 Ω. The resistance of the connecting wires can be ignored.

15 Ω

0,2 Ω

12 V

2 Ω

9 Ω 8 Ω

9.1 Calculate the current, I, that flows through the battery. (6)

9.2 How will the reading on the voltmeter be affected if the 9 Ω resistor is

removed and replaced with a conducting wire of negligible resistance?

Explain your answer. (4)

[10]

QUESTION 10

10.1 In the circuit below the AC source delivers alternating voltages at audio

frequency to the speaker.

8,2 Ω

15 Vrms 10,4 Ω

10.1.1 What is the peak voltage that the source can deliver? (2)

10.1.2 Calculate the average power delivered to the speaker. (6)

10.2 Alternating current is generated at power stations.

Name TWO advantages of AC transmission over long distances. (2)

[10]

QUESTION 11

The work function of three metals is shown in the table below.

METAL WORK FUNCTION (W0) in J

Aluminium 6,54 x 10-19

Zinc 6,89 x 10-19

Silver 7,58 x 10-19

11.1 Give a reason why different metals have different work functions. (1)

11.2 Light of wavelength 2,3 x 10-7 m is shone onto a metal X. The average

speed of the emitted electrons is 4,78 x 105 m·s-1.

Identify metal X by performing a relevant calculation. (6)

11.3 What conclusion about the nature of light is drawn from the photo-electric

effect? (1)

[8]

QUESTION 12

Two metal spheres on insulated stands carry charges of +4 μC and -6 μC respectively. The spheres are arranged with their centres 40 cm apart, as shown below.

12.1 Calculate the magnitude of the force exerted by each sphere on the other (4)

12.2 By what factor will the magnitude of the force in 12.1 change if the distance between the spheres is halved? (Do not calculate the new value of the force.) (2)

12.3 Calculate the net electric field strength at point P, 20 cm from the -6µC as seen in the sketch above. (6)

12.4 The spheres are now brought into contact with each other and then returned to their original positions. Now calculate the potential energy of the system of the two charges.

(5)

[17]

Total section B [125]

Total marks [[150]]

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

V

X

Y

+4µC

-6µC

P

40 cm

20 cm

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