### SECTION A (25 Marks)

Answer all the questions in this section in the spaces provided
1.

Figure 1 below shows an object O placed infront of a plane mirror

On the same diagram, draw rays to locate the position of the image I, as seen from the eye.

2 marks

2.

wo uncharged metal spheres P and Q on insulating stands are in contact as shown in figure 2.

A negatively charged rod brought near but not touching sphere Q.

The spheres are then separated, after which the rod is removed.

State and explain the sign of the charge on each sphere after separation

2 marks

3.

Calculate the amount of current flowing through a bulb if 300 coulombs of charge flows through it in 2 minutes

2 marks

4.

Figure 3 shows two similar razor blades one placed on a wooden block and the other on a soft iron block.

bar magnet was brought near each razor. State and explain what happens to the razor.

3 marks

5.

The figure 4 below shows a wire carrying current with magnetic field. Indicate on the diagram the direction of motion of AB of the wire when switch is closed.

1 marks

6.

If a concave mirror has a focal length of 10cm. Find two positions where an object can be placed to give in each case, and image twice the height of the object.

3 marks

7.

Figure 5 below shows the pattern of water ripples in a dam. What information about the depth of the dam at point X can you deduce from the pattern of the ripples?

1 marks

8.

A man is standing 85m from a cliff face infront and 170m from the cliff at his back. He whistles loudly and hears two echoes. Calculate the time interval between the two echoes (speed of sound in air 340m/s

2 marks

9.

State and explain what would happen to the brightness of the bulb when the switch is closed and water start to be heated in the circuit shown in figure 6 below.

2 marks

10.

Give a reason why tungsten is used in electric bulb filament

............................................................................................................................................................

1 marks

11.

Figure 7 shows a displacement – time graph for a wave moving from point A to B.

Determine the frequency of the wave.

...........................................................................................................................................................

2 marks

12.

Arrange the following waves in order of increasing frequencies; infrared, X-rays, microwaves and visible light.

1 marks

13.

State the reason why soft iron is laminated in transformers.

1 marks

14.

A diode D is connected to a source of alternating current as shown in the circuit below in figure 8.

etch a graph of the output voltage as seen on a CRO on the axes in figure 9 below.

3 marks

### SECTION B (55 Marks)

Answer ALL the questions in this section in the spaces provided.
15.

a) Figure 10 shows an experimental set up used to determine the focal length of a lens. It consist of a mounted lens, L, a screen, S a metre rule and an illuminated object.

Describe how the set up may be used to determine the focal length f, of the lens in figure 11

b) Figure 11 show a graph of the relationship between 1/u and 1/v

for a convex lens where u and v are object and image distances respectively.

From the graph, determine the focal length of the lens

c) Figure 12 show rays of light A, B and C incident on a glass –air interface at point O. A1 B1 and C1 are the corresponding emergent rays.

Determine i) The critical angle of the glass material.

.................................................................................................................................................. ..................................................................................................................................................

ii) The refractive index of the glass material.

..................................................................................................................................................

14 marks

16.

a) Figure 13 below shows a circuit consisting of four resistors of resistance 3, 2.5, 1 and 2 respectively, two ammeters , A1 and A2 connected to a battery of emf, E, 6V and internal resistance, r of 1

) Calculate the total external resistance in the circuit.
ii) Current through A1
iii) Current through A2

Figure 14 below shows an arrangement which may be used to charge a capacitor of capacitance 50µF and then to connect it to a capacitor of capacitance 20µF.

i) The switch S is first placed at position A, so that the capacitor C1 is connected to the 12V dc supply. Calculate the charge stored in the capacitor

ii) The switch S is now changed to position B. Calculate the final potential difference across the capacitors.

12 marks

17.

a) Give a reason why mains electricity is transmitted at very high voltage.

.................................................................................................................................................. ..................................................................................................................................................

b) The circuits in the figure 15 (a) and (b) shows “short circuits”. In both, the fuse had blown but whereas (a) is now safe (b) is still dangerous even though the lamp is out. What suggests the circuit is safe?

Explain..................................................................................................................................................

c) State one factors that determine magnitude of e.m.f induced in a coil. .................................................................................................................................................. ..................................................................................................................................................

d) Fig. 16 below shows an induction coil used to produce sparks.

11 marks

18.

a) Distinguish between hard and soft x-rays.

b) Figure 18 shows a circuit of a modern x-ray tube.

i) Name the parts labeled P and R

P.....................................................................................

R....................................................................................

ii) State the material used to make part Q, and give reason why the material is suitable. ............................................................................................................................................. .............................................................................................................................................

iii) How can the intensity of the x-rays in the tube be increased.

.............................................................................................................................................

c) Figure 19 shows a waveform displayed on the cathode ray oscilloscope screen when an alternating voltage is applied to the y- input. The time- base is set at 1ms/cm and the y- gain at 10v/cm

Calculate i) The amplitude of the ac input voltage

............................................................................................................................................. .............................................................................................................................................

ii) The frequency of the ac input voltage signal

.............................................................................................................................................

9 marks

19.

a) In an experiment of photoelectric emission from a clean metal surface the following graph was obtain

i) The threshold frequency of the metal surface given that the speed of light C=3.0 x108m/s ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

ii) Planck’s constant h given that electron charge, e =1.6 x 10-19C

............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

iii) The work function, Wo of the metal in electron volts. (1mk) ............................................................................................................................................. .............................................................................................................................................

b) The figure below shows the cross-section of a diffusion cloud chamber used to detect radiation from radioactive sources.

i) State the function of the following: I. Alcohol

................................................................................................................................

II. Solid CO2.

................................................................................................................................

ii) Explain briefly how the diffusion cloud chamber can be used to detect and identify alpha particles. .............................................................................................................................................

iii) Y -Intercept = 1.8ev.

(b) I Alcohol condenses around the ions formed by the radiation to form the narrow tracks.

II Cools the bottom of the chamber and also condenses alcohol below its normal temperature.

III Solid CO2 cools the bottom of the chamber, alcohol vaporizes and spreads throughout the chamber. It is cooled below its normal temperature in case of a radiation, air around the path of the radiation is ionized. Alcohol condenses around these ions to form a narrow cloud.

13 marks

Back Top