# Physics–Paper 2 June 1989

CARIBBEAN EXAMINATIONS COUNCIL

SECONDARY EDUCATION CERTIFICATE

EXAMINATION

PHYSICS

Paper 2

General Proficiency

1 1/4 hours

1. You MUST use answer this answer booklet when responding to questions. For each question, write your answer in the space provided and return the answer booklet at the end of the examination.
2. ALL WORKING MUST BE SHOWN in this booklet, since marks will be awarded for correct steps in calculations.
3. Attempt ALL questions.
4. The use of non-programmable calculators is allowed.
5. Mathematical tables are provided.

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO.

1. A transformer consists of a primary winding of 1,200 turns and a secondary winding of 300 turns. An experiment is performed in which a resistive load on the secondary is varied. The values of the secondary current Iand the corresponding primary current, Iare recorded and then plotted on a graph as shown in figure I below.

(a) Draw a circuit diagram for the experiment. Label the primary and secondary windings.

(3 marks)

(b) (i) Find, from the graph, the value of Iwhen Is= 1.00 A.

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(1 mark)

(ii) Determine the slope of the line and hence write an equation relating Iand Ip.

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(4 marks)

(iii) State and explain what you would have expected the equation to be if the transformer had been an ideal one.

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(3 marks)

(iv) What would have been the value of Ifor the ideal transformer when I= 1.00 A.

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(1 mark)

(c) Describe TWO measures you would take in the construction of a transformer to make its behaviour close to that of an ideal one.

(i)________________________________________________________________________________________________________________________________________________________

(ii)_______________________________________________________________________________________________________________________________________________________

(4 marks)

Total 16 marks

2.

The diagram above, drawn to scale, shows plane wavefronts before and after refraction at an air glass boundary.

(i) Find the refractive index of the glass for these waves. Clearly show on the diagram (Figure 2) all measurements made.

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(4 marks)

(ii) What is the value of the angle of incidence for these wavefronts.

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(1 mark)

(b) Light is incident at 60° at an air-water boundary and is refracted at 40°, as shown in Figure 3 below.

(i) Calculate the refractive index of water.

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(3 marks)

(iii) Draw a wavefront diagram to represent this refraction at an air-water boundary. (Your diagram need not be drawn to scale)

Mark, on the diagram, the size of the angle between the incident wavefronts and the boundary, and also between the refracted wavefronts and the boundary.

(5 marks)

(c) (i) The functioning of the human eye depends on refraction. Name the TWO parts of the eye where refraction takes place.

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(2 marks)

(ii) Explain why the amount of refraction at one of the two parts is much greater than that at the other.

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(1 mark)

Total 16 marks

3. (a) Potential energy may be considered to be the energy of state or position, whereas kinetic energy is energy of motion. Write YES or NO in EACH of the boxes below to show whether the system posses the energy indicated at the top of the column.

(4 marks)

(b) The mass of a car and its occupants is 900 kg. It is travelling at 90 km h-1 (25 m s-1). When it stops suddenly, its kinetic energy is converted to internal energy in the iron brake drums.

(i) Calculate the kinetic energy of the moving car.

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(2 marks)

(ii) Each of the four brake drums has a mass of 2.5 kg. Find the rise in temperature which occurs when the car is brought to rest. (Specific heat capacity of iron = 450 J kg-1 K-1).

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(3 marks)

(c)

When a car stops suddenly, a driver might hit the windscreen like the one in figure 4 above. With reference to Newton’s law of motion, explain:

(i) why this might happen

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(3 marks)

(ii) how the wearing of a seat-belt might prevent such an accident.

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(2 marks)

(d) A car, carrying a passenger, stops suddenly. Describe the energy changes which takes place as the passenger is brought to rest by his seat-belt.

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(2 marks)

Total 16 marks

4. (a) Complete the following statement by filling in EACH blank space with an appropriate word.

Most non-physicists think that a force is needed to keep an object moving. This corresponds with the ideas put forward by ________________ more than two thousand years ago. It was ________________ who, in the sixteenth century, first realised that this was not so, although the law stating that bodies move with constant ________________ unless acted upon by an __________________ force is named after ____________________. Physicists nowadays realise that objects usually need a force to keep them moving because their motions are opposed by ____________ forces.

(6 marks)

(b) A girl of mass 50 kg starts running along a straight level road and stops after 70 seconds. The variation of her speed with time is shown in Figure 5 below.

(i) Calculate the total distance the girl runs.

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(4 marks)

(ii) What is her acceleration over the first 20 seconds?

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(1 mark)

(iii) What is the magnitude of the force that produces this acceleration?

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(1 mark)

(iv) How does the force in (iii) above arise?

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(2 marks)

(c) Calculate the girl’s momentum after

(i) 10 seconds

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(1 mark)

(ii) 40 seconds

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(1 mark)

Total 16 marks

5. (a) Figure six below shows TWO bar magnets lying parallel, close to and opposite each other. The magnetic field lines are found to be as shown. Complete the figure by putting in the polarity of EACH of the magnets, and marking the field direction in the four blank spaces.

(3 marks)

(b) Insert the magnetic field lines in EACH of the arrangements shown at (i) and (ii) below.

(i)

(3 marks)

(ii) The arrangement below shows a soft iron ring placed between two magnets.

(2 marks)

(c) (i) An ordinary torch battery is connected to a moving coil loudpseaker. State how the coil will move.

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(ii) What would you expect to hear?

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(2 marks)

d)

A low voltage alternating alternating supply, a graph of which is shown in Figure 7(a) opposite, is connected to a loud speaker and a sound is heard.

(i) What is the frequency of the sound that is heard?

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(2 marks)

(ii) On the axes of Figure 7(b) on page 12, draw a graph to show how the applied voltage would vary with time if the sound were louder than that represented in 7(a), but of the same frequency.

(2 marks)

(iii) On axes of Figure 7(c) on page 12, draw another graph to show how the applied voltage would vary with time if the sound were higher in pitch than that represented in Figure 7(a), but of the same loudness.

(2 marks)

Total 16 marks

END OF TEST

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