# Physics Paper 3 Questions and Answers - KCSE Prediction Papers 2022

#### Instructions to Candidates

• Write your name and index number and school in the spaces provided above.
• Sign and write the date of examination in the spaces provided above.
• Answer ALL the questions in the spaces provided in the question paper.
• You are supposed to spend the first 15 minutes of the 2½ hours allowed for this paper reading the whole paper carefully before commencing your work.
• Marks are given for a clear record of the observations actually made, their suitability, accuracy and the use made of them.
• Candidates are advised to record their observations as soon as they are made.
• Non-programmable silent electronic calculators may be used.
• This paper consists of 8 printed pages.
• Candidates should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing.
• Candidates should answer the questions in English. ## Questions

Question 1
You are provided with the following:

• A metre rule
• A spring balance
• A mass of 200g ( 2N) with a hook or (two 100g masses)
• Stand
• Knife edge support.
• Two light strings about 10cm long.

Proceed as follows:

1. Using the string provided make two loops to be used as hooks L1 and L2 in the diagram.
2. Suspended the spring balance from a clamp and using one loop to support the rule from the spring so that the loop L2 is on 85cm mark.
3. Support the other end of the rule with a knife edge at the 10cm mark so that the rule is horizontal. 4. Using loop 1 suspended the 2N weight at a distance d=10cm from the knife edge as shown and take the reading of the spring balance, record the results in table 1.
5. Adjust the distance d to 20cm, 30cm e.t.c and each time recording the reading of the balance to complete the table.
Table 1
 Distance (d) 10.0 20.0 30.0 40.0 50.0 60.0 70.0 Force (N)
(7marks)
6. Plot a graph of force F against distance d(cm) (5 marks)

1. The slope (2mks)
2. The value of F when d=0 (2mks)
8. Using the information from your graph, determine the constant k and m in the equation below and state units, f represents the reading of the balance and d is as shown in the above. F=2md +40k. (4marks)

Question 2
PART A
You are provided with the following:

• Two new dry cells
• A resistor labeled Q
• Wire mounted on a millimeter scale
• 6 connecting wires with crocodile clips on one end of at least three
• A voltmeter
• An ammeter
• A switch

Proceed as Follows:

1. Connect the apparatus provided as shown in the figure below. 1. Take the voltmeter reading when the switch S is open.
V1= ……………………………… volts (1 mark)
2. Close the switch S, and take the voltmeter reading V2 and the ammeter reading I
V2 = ………………………………… volts (1 mark)
I1 = …………………………………... Amperes (1 mark)
3. Calculate the quantity P = V1 - V2 (2 marks)
I1
2. Set up the circuit as shown in the figure below 1. Take the voltmeter reading V and the ammeter reading I. (2 marks)
V = ………………………….
I = ……………………………
2. Determine the resistance R of Q (2 mark)
3. Set up the circuit shown in the figure below 4. Move the crocodile clip along the wire AB to a point such that L = 100cm. Note the voltmeter reading and record in table 2.
5. Repeat (d) above for values of L = 80cm, 60cm, 40cm, 20cm and 0 cm, tabulate your results. (5 marks)
Table 2
 Length L (cm) 100 80 60 40 1/L(1/cm) Voltmeter Reading (V) 1/v(1/V) Z = (1/L)/(1/v)  (V/cm)
6. Determine the average value of Z. (2 marks)
PART B
You are provided with the following
• A candle
• A lens and a lens holder
• A screen
• A metre rule
7. Determine the focal length, f by focusing a distant object.
f = …………………….cm (1mark)
8. Set up apparatus as shown in the figure below ensure that the candle flame and the lens are approximately the same height above the bench. 9. Set the position of the lens so that it is 40cm from the candle (u=40cm). Adjust the position of the screen until a sharp image of the candle flame is obtained. Measure the distance (v) between the lens and screen. Record the value of v in the table below.
10. Repeat the procedure in (i) above for the other values of u in the table 3 below. Complete the table (3marks)
Table 3
 U(cm) 40 50 V(cm) Magnification m = v/u    ## Confidential

• The information contained in this paper is to enable the head of school and teacher in charge of Physics to make adequate preparations for this year’s Physics joint practical examination. NO ONE ELSE should have access to this paper or acquire knowledge of its contents. Great care must be taken to ensure that the information herein does not reach the candidates either directly or indirectly.
• The Physics teacher is NOT expected to perform the experiments
• The apparatus required by each candidate for the Physics joint practical examination are set out on this page. It is expected that the ordinary apparatus of a Physics laboratory will be available.
• The Physics teacher should note that it is his/her responsibility to ensure that each apparatus acquired, for this examination agrees with specifications on this page.

Question 1
Provide each candidate with the following apparatus.

• A metre rule
• A spring balance
• A mass of 200g (2N) with a hook or (two 100g masses)
• A complete retort stand
• Knife edge support atleast 10cm high
• Two light strings about 10cm long.

Question 2

• Two new dry cells
• Cell holder
• 10 ohms resistor labeled Q
• 100cm of nichrome wire SWG 28 labeled AB at the ends mounted on a millimeter scale
• 6 connecting wires, atleast 3 with crocodile clips
• A voltmeter (0 – 5v)
• An ammeter (0 – 1A) of (0 – 2.5A)
• A switch
• A candle
• A lens of focal length 20cm and a lens holder
• A white screen
• A metre rule    ## Marking Scheme

1.  Distance (d) 10 20 30 40 50 60 70 Force (N) 0.8 1 1.2 1.2 1.8 2 2.4
±0.01 1mark for each correct value -max. 7mark
2. 3.
1. The slope
(0, 0.4) (70, 2.4) ½ mk for each change
=   2.0
70 x 10-2
= 2.857 N/cm 1mk for evaluation, with units ,4s.f or exact
Or 2.857 x 10-2 N/M
2. When d = 0, Force = 0.4N i.e the y – intercept
(1mk for identify it’s a value for y – intercept)
(1mk for correct reading from the graph)
4. Comparing y = mx +c with F = 2md +40k
2.857 = 2m
2.857= m
2
Y= intercept = 40k
= 0.4 = 40 k√1
40     40
= 0.04
40
N√1
1.
1.
1. V1 = 3.1 ± Volts  (1mk) (at least 1 d.p)
2. V2 = 2.6 ± 0.1V  (1mk) (at least 1 d.p)
I1 = 0.12 ± 0.02A  (1mk)
3. P = 3.1 - 2.6 (1mk)
0.12
= 4.167Ω
2.
1. V = 2.2 ±V 0.1  (1mk) (at least 1 d.p)
I = 0.22 ±0.02A  (1mk)
2. R =  2.2   = 10Ω
0.22
1mk for ohms law/ substitution
1mk correct evaluation with correct unit

1.  Temp L (cm) 100 80 60 40 1/L(1/cm) 0.01 0.0125 0.01667 0.025 Voltmeter Reading (V) 1.5 1.3 1.1 0.9 1/v(1/V) 0.6667 0.7692 0.9091 1.111 Z = (1/L)/(1/v)  (V/cm) 0.01496 0.01625 0.01834 0.0225
Allow both rounding off and truncation
• Correct conversion of 1/L  (1mk)
• Voltmeter Reading within range  (1/2mk each) to a max of 2mks
• Correct evaluation of 1/V  (1mk)
• Correct evaluation of Z  (1mk)
1. f = 20.0 ± 1.0 cm 1mk 1d.p a must

1.  U(cm) 40 50 V(cm) 41 34.0 Magnification m = v/u 1.025

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