### SECTION A (60 Marks)

Answer ALL the questions in this section
1.

The figure 1 below shows the image in front of a mirror M.

By ray diagram construction, locate the position of the object.

2 marks

2.

A negatively charged rod is brought rear the cap of a leaf electroscope. The cap is then earthed momentarily by touching with the finger. Finally the rod is withdrawn. The electroscope is found to be positively charged. Explain how this is acquired

2 marks

3.

Explain why the e.m.f of a dry cell drops if a large current is drawn for a short time and then recovers if allowed to rest.

2 marks

4.

Use the domain theory to explain how an unmagnetized piece of iron becomes magnetized when it is heated and then allowed to cool in a magnetized field.

2 marks

5.

A boy observes his face in a concave mirror of focal length 100cm. If the mirror is 80cm away, state one characteristics of the image observed

1 marks

6.

The coil of an electric motor is usually wound on a soft iron armature. State two purposes by this armature.

2 marks

7.

A student stands at a distance 400m from a wall and claps two pieces of wood. After the first clap the student claps whenever an echo is heard from the wall. Another student starts a stopwatch at the first clap and stops it after the twentieth clap. The stopwatch records a time of 50 seconds. Find the speed of sound.

3 marks

8.

The figure 2 below shows a displacement-time graph for a wave motion

2 marks

9.

Figure 3 below shows an incomplete circuit diagram for a half-wave rectification of an AC voltage

a) Complete diagram by inserting a diode at X so that the output terminals are positive and negative as shown

b) On the axes provided below sketch a graph showing how the output voltage varies with time

2 marks

10.

The element of an electric hot plate has a resistance of 80Ohms. What is the energy dissipated when the element is kept on for 20 minutes on a 240V supply

2 marks

11.

Describe how microwaves are used in determining distances of objects as in the radar.

2 marks

12.

The figure 5 below shows a series of wave fronts one wavelength a part approaching a gap between two barriers in ripple tank

Show on the figure 5 what happens as the waves pass through the gap .

1 marks

13.

In the figure 6, below if the critical angle of glass is 390 ,sketch on the diagram the path of a ray till it emerges from the prism.

2 marks

14.

Explain briefly how free electrons are produced in an X-ray tube

2 marks

### SECTION B (20 Marks)

Answer all the questions in this section.
15.

a) The refractive index of glass is2/3 and that of water is 3/4 Calculate the refractive index of glass with respect to water. ________________________________________________________________________

b) The figure 7 below shows a ray of light incident at an angle of 35.60 at point D on the first face of a glass prism ABC. The refractive index of the prism is 1.6.

Determine the angle of refraction at point D.

Find the angle of incidence of the refracted ray on the face AC to 1.d.p. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________

iii. Complete the diagram to show the emergent ray from the face AC

7 marks

16.

e LenzÃ¢â‚¬â„¢s law of electromagnetic induction

b) In the figure 8 below the bar magnet is moved into the coil.

c) State any two ways in which power is lost from the transformer and explain how each loss is minimized.

d) A transformer is used to provide a potential difference of 100KV to an X-ray tube from 250V a.c mains supply. A current of 100mA flows in the X-ray tube and the transformer is 100% efficient. Calculate; i. The ratio of the number of turns of the secondary coil to the number of turns in the primary coil.

____________________________________________________________________ ____________________________________________________________________

ii. The current in the primary coil ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________

iii. State giving reasons which of the coils of the transformer is thinner. ____________________________________________________________________

16 marks

17.

a) The figure 9 below shows an experimental set up in a vacuum for investigating the effect of a magnetic field on the radiation emitted by a radioactive source S.

15 marks

18.

. a) State two factors that determine the capacitance of a parallel plate capacitor ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________

b) Three capacitors of capacitance 100Ã‚ÂµÃ†â€™, 500aF and 400Ã‚ÂµÃ†â€™ are connected together in a circuit.

i. Draw a circuit diagram to show the arrangement of the capacitors which gives an effective capacitance of 250Ã‚ÂµÃ†â€™

________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________
c) The figure 11 below shows a circuit where a battery of e.m.f 6V a voltmeter, switches X and
Y, two capacitors of capacitance 2 Ã‚ÂµF and 4 Ã‚ÂµFare connected.

i. Determine the charge stored in the 2 Ã‚ÂµF capacitor when switch X is closed and switch Y is open. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________

ii. When switch Y is finally closed and switch X is open, determine the potential difference across each capacitor.

8 marks

19.

a) Distinguish between a real and virtual image

________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________

b) An object is placed 15cm from a converging lens of focal length 20cm. calculate the image position

c) In an experiment to determine the focal length of a converging lens, a graph of linear magnification M against image distance V was plotted as shown in figure 12 below.
graph

Use the figure 12 to determine the focal length of the lens ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________

d) i) Name the eye defect shown in the figure 13 below

12 marks