# Physics Paper 2 Questions and Answers - Maranda Post Mocks 2020/2021

SECTION A (25 MARKS)

1. Explain why sharp shadows support the theory that light travels in straight lines. (1 mark)
2. Give one reason why radioactive disintegration is different from ordinary chemical changes? (1 mark)
3. Figure 1 below shows part of a circuit containing three capacitors of 4μF, and 5μF and 6μF respectively.

Determine the p.d across the 5μf capacitor given that the total charge stored in the capacitors is 0.0000052 C (2 marks)
4. State one cause of power loss in long distance transmission wires and how these loses can be minimized (1 mk)
5. State the meaning of the term "threshold frequency" as used in photoelectric emission. (1 mark)
6. Figure 2 below shows the path of light passing through a rectangular block of perpex, placed in air.

Calculate the refractive index of the Perspex. (2 marks)
7. Two similar razor blades are placed one on a wooden block and the other on a soft iron block as shown in Figure 3 below.

It was observed that the razor blade on the wooden block was attracted to the magnet while the other on the soft iron block was not. Explain.(2 marks)
8. Figure 4 below shows two parallel current carrying conductors P and Q placed close to one another. Current flows in the opposite directions.

Sketch on the figure the magnetic field pattern formed by the two conductors. (1 mk)
9. The table in figure below shows part of the electromagnetic spectrum in order of decreasing wavelength.
 A B INFRA RED RADIATION VISIBLE LIGHT C D
1. How are waves C produced? (1 mk)
2. State one use of the wave D (1 mk)
10. A house has a lighting circuit operated from a 240V mains supply. Four bulbs rated 40W 240V and six bulbs rated 100W 240V are switched on for 5 hours a day. Determine the monthly bill for the consumer given that the cost of electricity is at shs.5.50 per unit (Take 1 month - 30 days and the standing charge is sh. 150) (2mks)
11. Figure 5 below shows an eye defect

Use a ray diagram to show how the defect above could be corrected. (2mks)
12. A girl standing at a distance claps her hands and hears an echo from a tall building 2 seconds later. If the speed of sound in air is 340m/s, determine how far the building is. (2mks)
13. A current-carrying conductor AB is in a magnetic field as shown in the figure below.

1. Indicate the direction of force F acting on the conductor (1 mk)
2. State two factors that determine the direction of the force F. (2mks)
14. Figure 6 below shows a wave form of voltage displayed on the screen of a C.R.O.

If the Y-Gain calibration is 7.5V per cm and the time base is 2.0 ms per cm.
Determine
1. The peak to peak voltage of the input signal. (2 mks)
2. The frequency of the signal. (1 mks)

SECTION B (55 marks)
Answer all questions in the spaces provided

1.
2. A radioactive isotope 23290T emits two alpha particles and two beta particles as a result of four successive disintegration. If the daughter product is represented as AZY. Work out the values of A and Z. (2 marks)
3. A certain radioactive material has the average count rate of 82 counts per second. After a time of 210 seconds, the count rate had dropped to 19 counts per second. The average background count rate remained constant at 10 counts per second. What is the half-life of the material?  (3mks)
4. Differentiate between nuclear fusion and nuclear fission as used in radioactivity (2mks)
5. State any two properties of beta particles (2mrks)
2.
1. Define the term electromagnetic induction (1 mark)
2. State two factors that determine magnitude of e.m.f induced in a coil. (2mrks)
3. State Lenz's a law of electromagnetic induction. (1 mark)
4. Figure 7 below shows a bar magnet being moved into a coil of insulated copper wire connected to a centre-zero galvanometer.

1. Show on the diagram the direction of induced current in the coil. (1mark)
2. State and explain clearly what is observed on the galvanometer when the S-pole of the magnet is moved into and then withdrawn from the coil. (2marks)
5. A transformer has 1000 turns in the primary and 50 turns in the secondary winding. The alternating e.m.f connected to the primary is 240V and the current is 0.5A. The transformer is 100% efficient. Determine the:
1. secondary e.m.f (2marks)
2. Current in the secondary winding. (2marks)
6. Figure 8 below shows a simple d.c generator.

The coil is rotated in a clockwise direction; indicate using an arrow on the figure the direction of the induced current as the coil passes the position shown. (1 mk)
3.
1.
1. What is the meaning of the term Photo-electric effect. (1 mark)
2. The minimum frequency of light which will cause Photoelectric emission from a metal surface is 5.6 x 1014Hz. If the metal surfaces irradiated with electromagnetic waves source of frequency is (6.8 x 1014Hz). Determine.
1. The work function of the metal surface (h=6.63 x 10-34 JS) (1 mk)
2. The energy of the source radiation. (2mks)
3. The maximum kinetic energy of the Photoelectrons produced in eV. (2mk)
2. Figure 9 below shows the variation of photoelectric current with applied voltage when two different surfaces a and b are illuminated with light a certain frequency. Use the information in the figure to answer the questions below.

1. State and explain between surface a and b which one has a higher work function (3 marks)
2. on the space provided sketch the graph of photoelectric current against applied voltage when light of two different intensity but same frequency is used to illuminate a given surface. (2mrks)
4.
1. State the Ohm's law (1mark)
2. You are provided with the following apparatus, a coil of nichrome wire, two dry cells, ammeter, voltmeter, connecting wires, switch and rheostat.
1. Draw a circuit diagram that can be used to verify Ohm's law (1mark)
2. Describe how the measurements obtained can be used to verify Ohm's law. (3marks)
3. Study Figure 10 below and answer the questions that follow

Determine:
1. The combined resistance (3 marks)
2. The total current flowing through the 6Ω resistor (2 marks)
3. Voltage across the 7Ω resistor (2marks)
5.
1.
1. Using a diagram explain how doping produces a p-type semi-conductor. (3 marks)
2. What is biasing? (1 mk)
3. The diagram below shows a circuit with a p-n junction and a very low power bulb.

State with reason the observations made on the bulb when the switch is closed. (2 mrks)
2.
1. what is rectification. (1 mk)
2. In the space provided below, draw a complete circuit to show half wave rectification. (2 marks)

## Marking Scheme

1. Sharp shadow is formed by blocking light traveling in a straight line.
2. Chemical reaction involves electrons while radio activity involves nuclear reaction ie neutron and proton. Or in chemical reaction no new element is formed while in radioactivity new element is formed.
3. v = Q/C
0.0000052 = 1.04V
0.000005
4. High resistance in the wire, this can be minimized by use of thick copper or aluminium wires.
5. This is the minimum frequency needed by a radiation to dislodge an electron from a given surface.
6. C = 42.5o, n = 1/c = 1/sin42.5 = 1.48
7. Soft iron being a magnetic material is induced with magnetic properties thus become magnetic which holds/attract the razor blade. Unlike wood which is not.
8.
9.

10.
 A-Radiowaves B - MIcrowaves C- U.V D- X-Rays
1. Produced by the sun
2.
• Used in medicine
• Industries
• In crystallography
11. (4 x 40)+(100 x 6) = 1600 + 600 = 2200W
760/1000 x 5 = 3.8 Kwh. daily
In one month = 3.8 x 30 = 14 KWh
Amount in Ksh = 150 + 114 x 5.50 = Ksh 777
12.
13. S = 2/2 x 340 = 340m
14.
1.
2.
• Direction of the magnetic field
• Direction of the current
15.
1. V = 7.5 x 1
=7.5V
2. 2.0 ms = 0.002s
T -> 2cm
T = 2 x 0.002
=0.004s
f = 1/t = 1/0.004s = 250Hz
16.
1.
• cosmic rays from outer space
• natural and artificial radio isotopes
• some rocks
2. 23290T -2β-23292A -2α- 22488Y
A = 224
Z = 88
3. Subtract average background from both initial and final count rate.
Initial 82 - 10 = 72
Final 19 - 10 = 9
72 -1- 36 -2- 18 -3- 9
Number of half-life is 3.
Thus half life period = 210/3 = 70 seconds
4. Nucliear fusion is the fusing/combination of nuclei to form heavier nucleus while nuclear fission is the splitting of the nucleus into nuclei.
5.
• They are streams of electrons
• They are negatively charged
• Can be absorbed by aluminum
• Greatly deflected by electric and magnetic field.
17.
1. This is the induction of current in an electric conductor due to change in magnetic field/flux.
2.
• the speed of rotation of the coil
• number of turns in the coil
• the strength of the magnetic field
3. It states that the direction of the induced e.m.f is such that the induced current which it causes to flow produces a magnetic effect that opposes the change producing it.
4.
1.
2. The galvanometer deflects to the left then right. The direction of  the induced current produces an electromagnet that opposes the motion of the magnet.
5.
1.
1. NS/NP = VS/VP
50/1000 = VS/240
Vs = (240 x 50)/1000 = 12v
2. NS/NP = IP/IS , 50/1000 = 0.5/IS
Is = (1000 x 0.5)/50 = 10A

18.
1.
1. Photoelectric effect is the emission of electrons from the surface of a solid when illuminated which electromagnetic radiation of sufficient frequency.
2.
1. Wo = hfo = 6.63 x 10-34 x 5.6 x 1014
=3.713 x 10-19 J
2. E = hf = 6.63 x 10-34 x 6.8 x 1014
=4.508 x 10-19J
3. K.E = 4.508 x 10-19 - 3.713 x 10-19 = 0.795 x 10-19 J
In eV, =
0.795 x 10-19 = 0.4969 eV
1.6 x 10-19
2.
1. b has a higher work function because from the graph b requires less stopping potential as compared to a showing that in b there is less kinetic energy left than in a.
2.
19.
1. The current flowing through a conductor is directly proportional to the potential difference across it provided the temperature and other physical conditions are kept constant.
2.
1.
2.
• Set the apparatus as shown above
• Vary the rheostat and record the corresponding values of voltages and current.
• Plot a graph of voltages against current
• The graph should be a straight line passing through the origin.
• In conclusion the current is directly proportional to the potential difference.
3.
1. 1/RT = 1/13 + 1/5 + 1/4 = 137/260
RT = 260/137 = 1.898 Ω
2. I = 3/13 = 0.23A
3. V = IR = 0.23 x 7 = 1.61V
20.
1.
1. To produce a p type semiconductor, a group 4 element such as germanium or silicon is doped using trivalent atom i.e group 3 element. The three electrons are used for bonding leaving a hole uncovered.
2. Biasing is the application of potential difference across a p-n junction.
3. When the switch is closed the bulb will light because the p-n junction is forward biasied.
2.
1. This is the conversion of an alternating voltage (ac) to a direct voltage (dc)

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