## Physics P2 Questions and Answers - Butula Sub-County Post Mock Exams 2021/2022

INSTRUCTIONS TO CANDIDATES

1. Write your name and index number in the spaces provided at the top of this page.
2. Sign and write the date of examination in the spaces provided above.
3. This paper consists of TWO sections: A and B
4. Answer ALL the questions in the sections A and B in the spaces provided.
5. ALL working MUST be clearly shown.
6. Non-programmable silent electronic calculators and KNEC mathematical tables may be used.

FOR EXAMINERS USE ONLY.

 SECTION QUESTIONS MAXIMUM SCORE CANDIDATE’S SCORE A 1 – 11 25 B 12 11 13 10 14 10 15 11 16 13 Total Score 80 ## QUESTIONS

SECTION A (25 marks)

1. The figure below shows two mirrors inclined at an angle of 80° to each other. A ray of light is incident on Mirror as shown below. 1. Complete the path of the ray as it emerges. (1 mark)
2. Indicate the angle of reflection on each mirror. (2 marks)
2. State the reason why the magnetic field strength of a magnet is greatest at the poles.(1 mark)
3. You are provided with; 1.0 μ F, 2.0 μ F and 3.0 μ F capacitors. Arrange the three capacitors with a cell such that the total capacitance is 1.5. (3 marks)
4. Fours pins were hang onto two magnets as shown. Identify the polarity on end X, Z, and Q. (3mks)
X: _______________________________________
Z:____________________________________
Q:________________________________
5. The Figure shows a cathode ray entering into a region between two charged plates. Complete the diagram to show the path of the ray in the field. (1 marks)
6. A form two student found the dry cells leaking on removing them from the torch. Name this defect and how is minimized. (2 marks) 1. Identify radiation K. (1 mark)
2. Determine the values of x and y. (2 marks)
8. The figure below shows a ray of light passing into a glass prism ABC. Sketch the path of the ray as it travels from face AC. (critical angle for glass is 42º) (2 marks)
9. An electric heater is rated 1000W, 240V. Calculate the resistance of this element. (3 marks)
10. The figure below shows electromagnetic spectrum.
1. Identify A. (1 mark)
2. State how A is detected. (1 mark)
11. Study the figure below and answer the question that follows. When switch is closed at x, the lamp lights but when switch is closed at Y, the lamp does not light. Explain this observation. (2 marks)
12.
1. Distinguish between rarefaction and compression. (1 mark)
2. The figure below shows a displacement (cm) time graph for a progressive wave. 1. State the amplitude of the wave. (1mark)
2. Determine the frequency of the wave. (2marks)
3. Given that the velocity of the wave is 320cm/s determine its wavelength (3marks)
3. A man standing600 away from a wall hangs two pieces of wood together and hears an echo 2.5 seconds later. Determine the speed of sound in air at that place. (3 marks)
4. State any one use of x- rays in medicine. (1 mark)
13.
1. State two factors that affect photoelectric emission. (2 marks)
2. Light of wavelength 4.3 x 10-7m is incident on two different metal surfaces, nickel and potassium.
(Take speed of light as 3.0 x 108 ms-1and planks constant h, as 6.63 x l0-34Js).
1. Determine the energy of the incident radiation. (3 marks)
2. If the work function of nickel is 8.0 x 10-19J and that of potassium is 3.68 x 10-19J, state with a reason from which of the two metals the given light will eject electrons. (2 marks)
3. Determine the velocity of the emitted electrons from the metal surface in b(ii). (Take the mass of an electron as 9.1 x 10-31 kg). (3 marks)
14.
1. Figure below shows an experimental set up consisting of a mounted lens, I, A screens, a metre rule and a candle 1. Describe how the set up may be used to determine the focal length f, of the lens. (3 marks)
2. State why the set up would not work if the lens were replaced with a diverging lens.(1 mark)
2. The Figure below shows an object in front of concave mirror and it’s image. 1. Locate position of its principal focus. (3marks)
2. If the figure is drawn to scale, determine the magnification. (2 marks)
3. State one reason why a convex mirror is preferred over a plane mirror for use as a driving Mirror. (1 mark)
15.
1. State Lenz’s law. (1 mark)
2. The diagram in the figure below shows a bar magnet attached to a spring oscillating through a coil connected to a galvanometer. 1. State and explain the observations made on the pointer of the galvanometer.(2 marks)
2. Explain why the oscillations dies off very fast. (1 mark)
3. The primary coil of a transformer has 1200 turns and the secondary coil has 60 turns. The transformer is connected to a 240V A.C source. Assume there are no energy losses, determine secondary voltage (2 marks)
4. The following figure shows a coil in a magnetic field. The coil is rotated in the direction shown by the arrow to produce an alternating current. 1. Name the parts labelled X. (1 mark)
2. State two factors that influence the magnitude of the induced e.m.f (2 marks)
5. State and explain any one ways by which energy losses are minimized in a transformer. (2 marks)
16.
1. Give a reason why power is transmitted at high voltage. (1 mark)
2. The cost of electricity in a region is sh.7.20 per kwh.
1. a 1.5KW water heater for 1 hour per day.
2. a 100W light bulb for 30 days at 12 hours per day and
3. a fan of resistance 24ohms connected to a 240V supply for 30 days at 2 hours per day.
1. What would be the monthly bill for a household using the above appliances? (3 marks)
2. In addition to the energy consumed, the company charges each customer the following.
1. a monthly standing charge of sh.150.00.
2. a fuel cost levy of 50 cents per kwh consumer.
3. a foreign exchange levy of 40cts per kwh.
4. a value added tax of 16% of the monthly energy consumption
Find the total monthly bill.(2 marks)
3. The figure below shows an electric circuit with two bulbs X and Y, which are identical. Explain what happens to the bulbs when:
1. S1 only is closed. (1 mark)
2. S1 and S2 are closed. (1 mark)
4. The figure below shows an electric circuit. Find
1. the effective resistance. (2 marks)
2. the current supplied by the battery (3 marks) ## MARKING SCHEME

SECTION A (25 marks)

1. The figure below shows two mirrors inclined at an angle of 80° to each other. A ray of light is incident on Mirror as shown below. 1. Complete the path of the ray as it emerges. (1 mark)
2. Indicate the angle of reflection on each mirror. (2 marks)
first r = 70º
r = 10º
2. State the reason why the magnetic field strength of a magnet is greatest at the poles.(1 mark)
within tha magnet, north and south poles of the dipoles cancel out but at the end of the poles they don't
3. You are provided with; 1.0 μ F, 2.0 μ F and 3.0 μ F capacitors. Arrange the three capacitors with a cell such that the total capacitance is 1.5. (3 marks)
1μ and 2μf in parallel
CT = (1 + 2) × 3
(1 + 2) + 3
= 9
6
= 1.5μf 4. Fours pins were hang onto two magnets as shown. Identify the polarity on end X, Z, and Q. (3mks)
X:south pole
Z:north pole
Q:north pole
5. The Figure shows a cathode ray entering into a region between two charged plates. Complete the diagram to show the path of the ray in the field. (1 marks)
6. A form two student found the dry cells leaking on removing them from the torch. Name this defect and how is minimized. (2 marks)
polarization - minimised using depolarize, manganese (IV) oxide or potassium diphromate 1. Identify radiation K. (1 mark)
2. Determine the values of x and y. (2 marks)
y = 228    x = 89
8. The figure below shows a ray of light passing into a glass prism ABC. Sketch the path of the ray as it travels from face AC. (critical angle for glass is 42º) (2 marks)
9. An electric heater is rated 1000W, 240V. Calculate the resistance of this element. (3 marks)
p = v2
R
1000 = 2402
R
R = 2402
1000
= 57.60L
10. The figure below shows electromagnetic spectrum.
1. Identify A. (1 mark)
infrared
2. State how A is detected. (1 mark)
blackened bulb thermometer,  skin
11. Study the figure below and answer the question that follows. When switch is closed at x, the lamp lights but when switch is closed at Y, the lamp does not light. Explain this observation. (2 marks)
when switch is at x, diode is foward biased thus allow current to flow.
when switch is at y, diode is reversed biased current does not flow
12.
1. Distinguish between rarefaction and compression. (1 mark)
rarefaction is a region of low pressure in the wave motion while compression is region of high pressure in the wave motion
2. The figure below shows a displacement (cm) time graph for a progressive wave. 1. State the amplitude of the wave. (1mark)
5 cm
2. Determine the frequency of the wave. (2marks)
period = 20s
f =
20
=0.05Hz
3. Given that the velocity of the wave is 320cm/s determine its wavelength (3marks)
v = λf
320 = 0.05λ
λ = 6400 cm or 64 m
3. A man standing600 away from a wall hangs two pieces of wood together and hears an echo 2.5 seconds later. Determine the speed of sound in air at that place. (3 marks)
speed = 2 × 680
2.5
= 480m/s
4. State any one use of x- rays in medicine. (1 mark)
identify fractures in bones
identify tumours in the soft tissues (any 1 x 1)
13.
1. State two factors that affect photoelectric emission. (2 marks)
work function of metal
2. Light of wavelength 4.3 x 10-7m is incident on two different metal surfaces, nickel and potassium.
(Take speed of light as 3.0 x 108 ms-1and planks constant h, as 6.63 x l0-34Js).
1. Determine the energy of the incident radiation. (3 marks)
E = hc
λ
= 6.63 × 10-34 × 3 × 108
4.3 × 10-7
= 4.626 × 10-19J
2. If the work function of nickel is 8.0 x 10-19J and that of potassium is 3.68 x 10-19J, state with a reason from which of the two metals the given light will eject electrons. (2 marks)
potassium
work function of potassium is less than the energy of incidence radiation E
3. Determine the velocity of the emitted electrons from the metal surface in b(ii). (Take the mass of an electron as 9.1 x 10-31 kg). (3 marks)
E = Wo + K.E
4.626 × 10-19 - 8.68 × 10-19 = 1/2 × 9.1 × 10-31
1/2 × 9.1 × 10-31 = 9.4558 × 10-20
= √9.4558 × 10-20 × 2
9.1 × 10-31
= 4.56 × 105 m/s
14.
1. Figure below shows an experimental set up consisting of a mounted lens, I, A screens, a metre rule and a candle 1. Describe how the set up may be used to determine the focal length f, of the lens. (3 marks)
place the candle at 0 cm mark. adjust screen until a sharp image is obtainede on the screen
Measure u and v ; record u and v. Reduce u by say 5 cm and obtain new values of u and v. Repeat the procedure to obtain several values of u and v. Record results on the table and draw a graph 1/u vs 1/v. The intercept on 1/v will give 1/f hence f can now be obtained.
2. State why the set up would not work if the lens were replaced with a diverging lens.(1 mark)
the image may not be focused on the screen
2. The Figure below shows an object in front of concave mirror and it’s image. 1. Locate position of its principal focus. (3marks)
2. If the figure is drawn to scale, determine the magnification. (2 marks)
v = 5.9
u = 3.1
m  5.9
3.1
= 1.90
or
errors if heights issued
m = 2.1
1.0
=2.1
accept both
3. State one reason why a convex mirror is preferred over a plane mirror for use as a driving Mirror. (1 mark)
wide field of view, wide angle/range
15.
1. State Lenz’s law. (1 mark)
the direction of induced e.m.f is such that the induced current it causes to flow produces a magnetic effect that opposes the change producing it.
2. The diagram in the figure below shows a bar magnet attached to a spring oscillating through a coil connected to a galvanometer. 1. State and explain the observations made on the pointer of the galvanometer.(2 marks)
the pointer moves from left to right through zero at the frequency of oscillation of the magnet. When magnet moves down, the magnetic flux cuts the coil inducing e.m.f in the coil. ointer deflects in one direction. The same result on the pointer but in different direction
2. Explain why the oscillations dies off very fast. (1 mark)
the induced e.m.f causes current flow in a direction such as to oppose the downward and upward movement causing the reduced oscilliation
3. The primary coil of a transformer has 1200 turns and the secondary coil has 60 turns. The transformer is connected to a 240V A.C source. Assume there are no energy losses, determine secondary voltage (2 marks)
vs = ns
vp    np
vs = 60
240  1200
vs = 12v
4. The following figure shows a coil in a magnetic field. The coil is rotated in the direction shown by the arrow to produce an alternating current. 1. Name the parts labelled X. (1 mark)
split ring
2. State two factors that influence the magnitude of the induced e.m.f (2 marks)
strength of magnetic field
number of turn of a coil
rate of change of magnetic flux
5. State and explain any one ways by which energy losses are minimized in a transformer. (2 marks)
use of iron core to minimise energy losses by hysteresis
use thick copper wire to minimise energy loss by copper heating
flux leakage is minimised by winding secondary coil over primary coil
16.
1. Give a reason why power is transmitted at high voltage. (1 mark)
minimise power loss through resistance in the wire coil
2. The cost of electricity in a region is sh.7.20 per kwh.
1. a 1.5KW water heater for 1 hour per day.
2. a 100W light bulb for 30 days at 12 hours per day and
3. a fan of resistance 24ohms connected to a 240V supply for 30 days at 2 hours per day.
1. What would be the monthly bill for a household using the above appliances? (3 marks)
(1.5 × 1 + 100 × 12 × 30 + 2402 × 30 × 2)
1000                    24      1000
1.5 + 36 + 144 = 181.5
181.5 × 720 = 130 6.8/=
2. In addition to the energy consumed, the company charges each customer the following.
1. a monthly standing charge of sh.150.00.
2. a fuel cost levy of 50 cents per kwh consumer.
3. a foreign exchange levy of 40cts per kwh.
4. a value added tax of 16% of the monthly energy consumption
Find the total monthly bill.(2 marks)
1306.8 + 150 + 181.5 × 50 + 181.5 × 40 + 16 × 1306.8
100               100  100
= 4647.24/=
3. The figure below shows an electric circuit with two bulbs X and Y, which are identical. Explain what happens to the bulbs when:
1. S1 only is closed. (1 mark)
x and y light with some brightness. some current flows through the bulb
2. S1 and S2 are closed. (1 mark)
x lights brightly, y does not light . no current flows through y since it is short circuit
4. The figure below shows an electric circuit. Find
1. the effective resistance. (2 marks)
RT = 4 × 12 + 7
4 + 12
= 10Ω
2. the current supplied by the battery (3 marks)
I = V
R
= 20
10
= 2A

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