# Physics Paper 2 Questions and Answers - 2021 KCSE Eldoret Diocese Mock Exams

## Questions

INSTRUCTIONS:
• This paper consists of TWO Sections: A and B.
• Answer ALL the questions in sections A and B in the spaces provided.
• ALL workings MUST be clearly shown.
• Mathematical tables and electronic calculators may be used.

Section I (25 marks)

1. Figure 1 shows a pencil lying in front of a plane mirror. The pencil is moved 2cm towards the mirror in the same orientation.

Figure 1
Determine the distance between the new position of the tip of the pencil and its image. (2mks)
2.
1. State the basic law of magnetism. (1mks)
2. Figure 2 shows two bar magnets, one whose poles are labelled and a second one whose poles are labelled X and Y. Iron nails are attracted to the lower ends of the magnets as shown. (1mk)

Figure 2
Identify pole X
3. State the reason why convex mirror is preferred over a plane mirror for use as driving mirrors in cars. (1mk)
4. Figure 3 shows the displacement-time graph for a certain wave.

Figure 3
1. Determine the frequency of the wave. (2mks)
2. On the same diagram, draw a wave with half the amplitude and twice the frequency of the one shown. (1mk)
5.
1. State the main difference between primary chemical cells and secondary chemical cells. (1mk)
2. State how the design of a dry Lechlanche cell reduces polarization. (1mk)
6. Figure 4 shows a wave incident on a narrow opening.

Figure 4
Draw the appearance of the wave after passing through the opening. (1mk)
7. A student stands between two classroom walls and claps. After 0.6 seconds, she hears the first echo and hears the second echo after 0.8 seconds. Determine the distance from the student to the further wall. Take speed of sound in air = 320m/s. (3mks)
8. The list below is some radiations in the electro-magnetic spectrum. Red light, Gamma rays, Ultra violet radiations and Blue light. Arrange the radiations in order of increasing wavelength. (1mk)
9. A controlled amount of pentavalent (donor) impurity atoms added in to a pure semi conductor such as silicon to improve its conductivity.
1. Give name to the process above. (1mk)
2. What type of semiconductor is obtained in the above process? (1mk)
10. Figure 5 shows the cross-section of two bar magnets and a current carrying conductor held between them. The direction of current is into the paper.

Figure 5
1. indicate with an arrow the direction of force experienced by the conductor. (1mk)
2. State one way in which the force on the conductor above can be reduced. (1mk)
11.
1. State the reason why electrical power is transmitted over long distances at very high voltage and low current. (1mk)
2. An electric bulb is labelled 100W 20V. Determine the resistance of its filament at its operating temperature. (2mks)
12.
1. State Ohm’s law. (1mk)
2. Figure 6 shows an electrical circuit.

Figure 6
Determine the Ammeter reading in a closed circuit. (2mks)

SECTION B (55 Marks)

1.
1. State Lenz’s law of electromagnetic induction. (1mk)
2. Figure 7 shows stationary magnet and a solenoid being moved as shown.

Figure 7
1. State with a reason the direction of deflection of the galvanometer. (2mks)
2. State one way through which the size of deflection of the galvanometer can be decreased. (1mk)
3. State how energy losses in a transformer through eddy currents is minimized in its design.(1mk)
4. Figure 8 shows two identical coils C and D made of insulated copper wires and are placed close to each other. Coil C is connected to DC power supply and Coil D to a galvanometer.

Figure 8
1. State and explain what would be observed on the galvanometer immediately switch S is closed and then opened. (2mks)
2. How would the observation made in d(i) differ if the number of turns in coil C were doubled but those in D remain unchanged? (1mk)
5. The primary coil of a transformer has 250 turns and the secondary coil has 50 turns. The primary coil is connected to a 120V AC supply.
1. State with a reason the type of transformer described above. (1mk)
2. Determine the voltage in the secondary coils. (1mks)
3. Given that the current in the primary coil is 0.50A and in the secondary coil is 2.0A. Determine the efficiency of the transformer. (2mks)
2.
1. State the law of electrostatic charges. (1mk)
2. Figure 9 shows a highly positively charged glass rod being brought slowly near the cap of a negative charged gold leaf electroscope. It is observed that the leaf initially falls and then rises.

Figure 9
Explain this observation. (1mks)
3. Figure 10 shows an electric circuit used to charge a capacitor C. When switch is closed, it is observed that, the millimeter records some current which gradually reduces to zero with time.

Figure 10
Explain the observation (1mks)
4. Figure 11 shows an electrical circuit with three capacitors of 10μF, 2μF and 3μF capacitance connected to a 240V supply.

Figure 11
Determine
1. The effective capacitance of the capacitor combination. (2mks)
2. The charged stored in the circuit. (2mks)
3. The potential difference across the 2μF capacitor (2mks)
3.
1. State one condition necessary for total internal reflection to occur. (1mk)
2. Figure 12 (a) shows a ray of light travelling in an optically denser medium to an optically rarer medium. The angle of incidence i and angle of refraction r are also shown.

Figure 12 (a) & Figure 12 (b)
Complete Figure 12 (b) to show the path of refraction ray when the angle of incidence is increased to reach critical angle. (1mk)
3. An optical pin placed at the bottom of a glass measuring cylinder filled with a liquid and appears to be 11.4cm below the surface of the liquid. If the refractive index of the liquid is 1.48. Determine The height of the column of the liquid in the measuring cylinder. (2mks)
4.
1. State one reason why glass prisms are preferred to plane mirrors in their use in periscope. (1mk)
2. Figure 13 shows two right angled glass prism arranged to be used in a periscope.
An object is placed besides one prism as shown.

Figure 13
Complete the diagram by showing the path of rays of light from the object until they reach the eye. (1mk)
5. In an experiment to determine the focal length of a lens, you are provided with the following apparatus.
- A converging lens and a lens holder
- A lit candle
- A metre rule
- A white screen
1. State one measurements that you would take in the experiment. (1mk)
2. In another experiment similar to the above, a graph showing the relationship between 1/v and 1/u was plotted as shown in figure 13.

Use the graph to determine the focal length, f of the lens. (2mks)
6. Figure 14 shows a defeat of the eye

Figure 14
1. State two possible causes of the defect. (2mks)
2. Explain how the defect is corrected. (1mk)
4.
1.
1. In an X-ray tube explain why
1. The anode is made up of copper. (1mk)
2. The cathode and the anode are connected to a high potential difference between them. (1mk)
2. State the adjustments made in an X-ray tube in order to decrease the intensity of X-ray. (1mk)
3. State the property of X-rays that makes it used in detecting foreign objects in human bodies. (1mk)
2.
1. Explain the meaning of the term photoelectric effect. (1mk)
2. A monochromatic light frequency 6.25 x 1014 Hz is incident on a metal surface. The minimum frequency that can cause photo emmission on the metal surface is 5.5 x 1014Hz. Given that Planck’s constant, h is 6.63 x 10-34 Js.
Determine
1. The energy of the source light. (2mks)
2. The work function of the metal surface. (2mks)
3. The average kinetic energy of the photo electrons. (2mks)
5.
1. Figure 15 shows some features of a cathode ray tube.

Figure 15
1. Name parts E & F (2mks)
2. The process through which electrons are produced. (1mk)
2.
1. Alpha (α) particles cause more ionization in a gas compared to Beta (β) particles. Give one reason for this. (1mk)
2. The following is part of radioactive decay series. The symbols do not represent the actual symbols of the nuclides.

Determine the values of a and b (2mks)
3. A radioactive Isotope has a halflife of 5.25 years. Determine the fraction of the original mass in a sample that will remain after 42 years (2mks)

## Marking Scheme

1. New object distance = 5 – 2 = 3cm
Distance between tip and its image = 3 + 3 ✓
= 6cm✓

2.
1. Like poles repel, unlike poles attract. ✓
2. Pole X is South pole ✓

3. Convex mirror gives a wider field of view of✓the rear (behind) compared to plane mirror.

4.
1. Period, T = 8.0 x 10-4S✓
Frequency =       1         =         1
period           8.0 x 10-4
= 1250
= 1.25 x 103 Hz
2.
5.
1. Primary cells cannot be recharged after use while secondary cells can be recharged after use. ✓
2. Polarization is reduced by adding a depolarizer
or
6.

7. 2 Distance = Speed x time✓ (2d = vt)
2x = 320 x 0.8 ✓
x = 320 x 0.8
2
x = 128m ✓

8. Gamma rays, Ultra violet, Blue light, Red light
Increasing wavelength ✓

9.
1. Doping ✓
2. N – Type semiconductor ✓

10.
1.
2. Reduce the amount of current. ✓
or
Reduce magnetic field strength.

11.
1. To reduce power losses ✓
2. P=VI
I = P/V
= 100/20
= 5A
R = V/I ✓
= 20/5
= 4 Ω

Or
P = (V2 )/R
= V2/P
= 202/100
= 400/100
= 4 Ω
I = V/I ✓
= 20/5
= 4 Ω

Or
P=VI
I = P/V
= 100/20
= 5A
P =I2 R✓
R = P/I2
R = 100/25
= 4 Ω

12.
1. The current flowing through a conductor is directly proportional to the potential difference across the conductor provided Temperature and other physical conditions are kept constant. ✓
2. Effective Resistance = (3 x 6)/(3+6)
= 18/9
= 2 Ω
V = IR
I = V/R✓ = 5/2 = 2.5A ✓

13.
1. The direction of induced current is such as to oppose the change causing it. ✓
2.
1. Deflects to the right handside ✓Because by Lenz’s law, end A of the solenoid produces a South pole and there current is flowing in direction X to Z. ✓
2. -Decreasing the strength of the magnet
-Decreasing the number of turns in the solenoid.
-Decreasing the speed at which the solenoid moves.
Any ✓
3. The core is made up of thin sheets of insulated soft iron plate (ie. Core is laminated) instead of using a block of iron core✓
4.
1. The galvanometer deflects in one direction and goes back to zero when switch is closed. ✓
When the switch is open the galvanometer deflects in the opposite direction then to zero. ✓
2. The deflection would be smaller.
5.
1. Step down transformer. Because the number of turns in the primary coils are more than the number of turns in secondary coils. ✓
2. N_S/N_P = VS/VP
VS = 50 x 120/250
50/250= VS/120 = 24V✓
3. Power in primary =VPIP
= 120 x 0.5
= 60W
Power in secondary = VS x IS
= 24 x 2
= 48V
Efficiency = Powerout/Powerinpout x 100%✓
= 28/60 x 100%
= 80% ✓
14.
1. Like charges repel, unlike charges attract. ✓
2. As the rod approaches the cap, the positive charges initially attracts the negative charges on the leaf and plate before the leaf falls. ✓ As the rod is brought nearer, net positive charges are induced on the leaf and plate, where they repel each other making the leaf rise again. ✓
3. The milliameter record current as the capacitor is charging. ✓ When the capacitor is fully charged, it offers an equal P.d in the opposite direction therefore no current flows. ✓
4.
1. 2 + 10
= 12μF✓
CT = 3 x 12/3+12
= 36/15
= 2.4μF✓
2. Q = CV
= 2.4 x 240✓
= 576 μC
= 5.76 x 10-4 C✓
3. V = Q/C✓
= 576μC/12 μF
= 48V✓
15.
1.
1. The ray of light must be travelling from an optically denser medium to an optically rarer medium.
The angle of incidence must be greater than the critical angle. Any ✓
2.

3. η = Realdepth/Apparentdepth✓
Height = Real depth = n x Apparent depth
= 1.48 x 11.4
= 16.872cm ✓
4.
1. – The mirror absorbs some incident light while the prism does not.
- The mirror silvering peels off but this does not happen in prism.
- The mirror is thick and produces multiple images unlike prism.

Any ✓
2.
5.
1. – Object distances, u, using a metre rule. ✓
- A image distance, V, using a metre rule. ✓ any
2. Extrapolate the graph to cut either 1/V or 1/u axis or both.
At 1/Vintercept, 1/u = 0
.: 1/f = 1/V , 1/f = value of 1/V intercet
f = 1/(Valueof 1/V intercest) = 1/0.25✓
or f = 4cm
At 1/u intercept, 1/V = 0
.: 1/u= 1/f f = 1/0.25 = 4cm
6.
1. – Too short eyeball ✓
- Lens with too long focal length✓
2. By wearing converging lens spectacles. ✓
16.
1.
1. I – Copper is a good conductor of heat and therefore conducts heat produced. ✓
II – To accelerate electrons from the cathode to the anode. ✓
or
To give electrons sufficient kinetic energy.
2. Decrease the amount of heating current in the filament. ✓
3. X-ray penetrate more in less dense material and penetrate less in denser materials. ✓
2.
1. The emission of electrons from a metal surface when the metal surface is irradiated with electromagnetic radiation.
1.  E = hf
= 6.63 x 10-34✓ x 6.25 x 1014
= 4.14373 x 10-19 J✓
2. Wo = Hfo
= 6.63 x 10-34✓x 5.5 x 10-14
= 3.6465 x 10-19 J✓
3. – KE = hf ¬- Wo
= (4.14375 – 3.6465) x 10-19✓
= 0.49725 x 10-19
= 4.972 x 10-20 J✓
17.
1.
1. E – Filament ✓
F – Y – Plate✓
2. Thermionic emission✓
2.
1. Alpha particles have higher charge (+2) ✓
Compared to Beta particles (-1)
Alpha particles are heavier compared to Beta particles.
Any ✓
2. a = 234✓
b = 84 – 2 = 82 ✓
3. 5.25/42= 1/8
N/No = (1/2)T/t
N/No= (1/2)42/5.25
N/No=(1/2)8
= 1/256

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