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# Form 3 Physics Paper 1 End of Term 3 Exams 2021

Class: Form 3

Subject: Physics

Level: High School

Exam Category: Form 3 End Term 3 Exams

Document Type: Pdf

## Exam Summary

Answer ALL the questions in the spaces provided

SECTION A (25MKS)
1. In an experiment to determine the density of liquid X, a student obtained the following date:
- Mass an empty density bottle = 55.0g.
- Mass of the density bottle + water = 80.0g.
- Mass of the density bottle + liquid x = 70g.
Determine the density of liquid x (density of water is 1000kg/m3) (3mks)

2. A stick of legible weight is kept in a horizontal position by the force shown in the diagram below.

Calculate the value of y and the magnitude of force Q. (3mks)

3. State one way of increasing surface tension. (1mk)

4. Distinguish between Brownian motion and diffusion. (1mk)

5. i) Table below shows results of an experiment carried out to study properties of a spring.

State with a reason whether the experiment was done within the elastic limit of the spring. (1mk)

ii) An object of weight 20N is attached at the end of spring causes an extension of 0.05cm on the spring. Determine the spring constant. (2mks)

6. Explain how the area of support affect the stability of a body. (1mk)

7. The figure below shoes a Bunsen burner.

Explain how air is drawn into the burner when the gas tap is opened. (3mks)

8. A vacuum pump was used to pump out air from the glass immersed in liquids as shown below

After sometime the level of water rose to position X. Mark Y the corresponding position for the paraffin level. Give a reason for your answer. (2mks)

9. When a liquid is heated in a glass flask, it is observed that the level at first goes and then rises. Explain the observation. (2mks)

10. Give two ways of increasing sensitivity of a clinical thermometer. (2mks)

11. State one way in which the centripetal force on a body of mass (m) can be increased. (1mk)

12. A boy catches a cricket’s ball of mass 0.15kg moving at a velocity of 40m/s. Show that it hurts the boy more in trying to stop the bass in 0.01sec than stopping it in 0.5 sec. (3mks)

SECTION B (55 Marks)
13a i). State the meaning of the term critical angle as applied in refraction of light. (1 mark)

ii) The figure shows a ray of light incident on a glass-air interface.

i).Show on the diagram the critical angle, c. (1 mark)

ii) Given that the refractive index of the glass is aηg, and that the critical angle c = 42º, determine the value of is aηg. (3 marks)

(b) The figure shows an experimental set up consisting of a mounted convex lens L, cardboard screen with cross-wires at the centre, a plane mirror, a metre rule and a candle.

Describe how the set-up may be used to determine the focal length, f, of the lens. (4 marks)

14. The figure below shows an electromagnetic relay being used to switch an electric motor on and off. The electromagnet consists of a coil of wire wrapped around a core. The motor in figure is switched off.

(a) Suggest suitable material for the core. (1mark)

(b) What happens to the core when switch S is closed? (2marks)

(c) Why do the contacts A and B close when the switch S is closed. (2marks)

(d) When the switch S is opened, what will happen to;
(i) The core (1mark)

(ii) Soft iron armature. (1mark)

f).Give one other application of an electromagnet. (1mark)

(h) State two ways in which an electromagnet could be made more powerful. (2marks)

15. a) State Ohms’ law. (1mk)

b) Figure shows a graph of the relationship between potential differences, V (V) and current,

(i) State with a reason whether the device is ohmic or non – ohmic. (1 mks)

(ii) Determine the voltage when the current is 2.5 A (2 mks)

c) Figure – shows two resistors connected to a power supply.

Determine,
i).The effective resistance. (2 marks)

(ii) The ammeter reading if the voltage across the source is 3.75 V. (2 marks)

(d) State the reason for the following.
(i) In a filament bulb, air is removed and the bulb is filled with an inactive gas. (1 mk)

(iii) A fuse is made of a material with low melting point. (1 mk )

16. a) State one example of longitudinal wave. (1 mk)

b) Figure – shows how the displacement of a certain wave varies with time.

Determine the frequency of the wave. (2 marks)

c) Figure – shows two identical loud speakers L1 and L2 producing some sound and placed at an equal distance from a path AB.

(i) A passerby walks along path A B and hears alternating loud and soft sounds.
State the reason for loud sound. (1 mk)

ii).State the observation made when one of the loud speaker is replaced with another speaker
producing sound at a higher frequency. (1 mk)

d) State one condition for the formation of a stationary wave. (1 mk )

e) Figure – shows water wave fronts incident on an opening AB

i).On the same diagram sketch the wave fronts obtained after the waves passes the opening AB. (1 mk)

(ii) State one difference that would be observed on the wave if the opening AB was reduced to a narrow opening. (1 mk)

17. (a) State Snell’s law of refraction. (1mark)

(b) In an experiment to determine the refractive index of a liquid, the liquid was poured into a measuring cylinder, a pin was placed at the bottom of the cylinder and another pin used to locate the apparent position of the first pin. The values of real and apparent depth were used to plot a graph as shown below.

i).From the graph determine the refractive index of the liquid. (4 marks)

(ii) Given that the velocity of light in vacuum is 3.0 x 108 m/s, what would be the velocity of light in the liquid above. (4marks)

(c) The diagram below shows a ray of light incident on a glass-air interface.

Given that the refractive index of glass is 1.4, determine the value of θ (4marks)

d).State two conditions necessary for total internal reflection to occur. (2marks)

e) The diagram below shows a ray of light incident a glass prism ABC at 900

Complete the ray to show how it emerges from the prism given the critical angle of the glass is 420. (3marks)