# Physics Paper 3 Questions and Answers - Maranda High Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

• Answer ALL the questions in the spaces provided in the question paper
•  You are supposed to spend the first 15 minutes of the 2 ½ 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.
• Non-programmable silent electronic calculators and KNEC Mathematical tables may be used except where stated otherwise.

QUESTION 1

You are provided with the following: -

• 2 new size D dry cells
• A cell holder
• A switch
• An ammeter
• Five connecting wires
• Wire mounted on the metre rule labelled X
• A micrometer screw gauge (to be shared)
• A Voltmeter
Proceed as follows
1. Measure the diameter of the wire three times and determine the average diameter,
d ……………….……………………………………… mm (1 mark)
d………………………………………………………….. m (1 mark)
2. Determine the cross-section area of the wire,
A………………………………………………………….. m2 (1 mark)
3. Connect the circuit as shown in the figure 1 below. 4. Measure the voltage Efrom the Voltmeter, before closing the switch.
E = .......................................................................... V (1 mark)
5. Adjust the length, lof the wire to 0.20m, close the switch, S and read the value of current and record in the table 1 below.
Table 1
 Length, L (m) 0.20 0.30 0.40 0.50  . 0.60 0.70 Current, I (A) 1/L (A−1)
6. Repeat the procedure in (e) above for the values of lengths given. (6 marks)
7. Calculate the value of 1/L and record in the table above. (1 mark) (
8. On the grid provided plot a graph ofI1/L(y axis − ) against L (m) (4 marks)
9. Determine the gradient of the graph. (2 marks)
10. Given that the equation 1/L = P/EAL + r/E  holds for the graph, determine the value of ρ and r   (3 marks)

QUESTION 2

PART A

You are provided with the following:

• A lens and a lens holder.
• A screen with cross wires
• A candle
• A metre rule.
Proceed as follows:
1. Arrange the lightened candle, the lens and the screen as shown in figure 2. Adjust the position of the screen until a sharp inverted image of the candle is formed on the screen. 1. Measure the image distance v
v =  …………………………… cm (1 mark)
2. Determine the focal length of the lens using the formula
f =   uv      (2 marks)
u + v
2. Now arrange the lighted candle, the screen with cross wires and the lens as shown in figure 3. Ensure that the centre of the lens, the cross-wires, and the candle flame lie on the same horizontal line. The candle flames should be placed close to the cross-wires for better illumination. 1. Adjust the position of the lens until a sharp image of the cross-wire is formed on the screen next to the cross wires. (Hint: You have to rotate the lens slightly about a vertical axis so that the image of the cross-wires falls on the screen next to the cross wires and not on the cross-wires.)
Measure the distance d, between the lens and the screen.
d=………………………………. cm (1 mark)
2. Determine the values of L and X:
1. L =   df      (2 marks)
f − d
2. X =  + 1 (2 marks)
2f

PART B

You are provided with the following:

• A metre rule
• A knife edge
• One 50g mass and a 100 g mass
• Two pieces of threads each 30 cm long
• Some water in a beaker
• Liquid L in a beaker
• Tissue paper

Procced as follows

1. Balance the metre rule on the knife edge and record the reading at this point
Balance point = ……………………………………cm mark (1 mark)
For the rest of this experiment the knife edge must be maintained at this position.
2. Set up the apparatus as shown in the figure 4
Figure 4 The balance is obtained by adjusting the position of 100g mass when 50g mass is fully immersed in water. Record the values of X and D.
X =…………………………………………………… (1 mark)
D =…………………………………………………… (1 mark)
3. Using the principle of moments;
1. determine the weight W1of the 50g mass in water (2 marks)
2. determine the Upthrust UW in water (1 mark)
4. Remove the 50 g mass from the water and dry it using a tissue paper.
Keeping D constant, adjust the position of 100g mass until the metre rule is balanced and record the value of distance X when the 50g mass is fully immersed in liquid L.
X =…………………………………………………….. (1 mark)
1. Determine the weight W2 of the 50g mass in liquid L. (2 marks)
2. Determine the Uphtrust UL in the liquid. (1 mark)
5. Determine the relative density R.D of the liquid L, given that R.D = UL  (1 mark)
UW
6. Find the density of liquid L in S.I unit (1 mark)

CONFIDENTIAL

QUESTION 1

Each candidate to be provided with the following:
• 2 new size D dry cells in a cell holder
• A switch
• Seven connecting wires at least two with crocodile clips
• Voltmeter 0-3V or 0-5V
• Ammeter 0-2.5A
• Nichrome wire mounted on a mm scale labelled X
• A micrometer screw gauge (to be shared)

QUESTION 2

PART A

Each candidate to be provided with the following apparatus
• A lens of focal length 10 cm and a lens holder.
• A screen with cross wires
• A white screen
• A candle
• A metre rule.

PART B

Each candidate to be provided with the following apparatus:
• A metre rule
• A knife edge
• One 50g mass and a 100 g mass
• Two pieces of threads each 30 cm long
• Some water in a beaker
• 200ml of kerosene in a beaker labelled Liquid L
• Tissue paper

### MARKING SCHEME

QUESTION 1

You are provided with the following: -

• 2 new size D dry cells
• A cell holder
• A switch
• An ammeter
• Five connecting wires
• Wire mounted on the metre rule labelled X
• A micrometer screw gauge (to be shared)
• A Voltmeter
Proceed as follows
1. Measure the diameter of the wire three times and determine the average diameter,
d ……………0.30 ± 0.04  ✓1….……………………………………… mm (1 mark) 2 d.p a must
d…………0.30/1000  ✓½ = 3.0 × 10−4  ✓½……………………………………………….. m (1 mark) Working must be shown( students value to be used)
2. Determine the cross-section area of the wire,
A……22/7 × (1.5 × 10−4)2  ✓½ = 7.071 × 10−8 ✓½………………………………………………….. m2 (1 mark) Working must be shown
3. Connect the circuit as shown in the figure 1 below. 4. Measure the voltage Efrom the Voltmeter, before closing the switch.
E = ............3.0 ± 0.2.. ✓½............................................................ V (1 mark) 1 d.p a must
5. Adjust the length, lof the wire to 0.20m, close the switch, S and read the value of current and record in the table 1 below.
Table 1
 Length, L (m) 0.2 0.3 0.4 0.50  . 0.6 0.7 Current, I (A) 2 d.p  ±0.02 0.6 0.52 0.44 0.40 0.36 0.32 1/L (A−1) 1.667 1.923 2.273 2.500 2.778 8.333
6. Repeat the procedure in (e) above for the values of lengths given. (6 marks)
7. Calculate the value of 1/L and record in the table above. (1 mark)
8. On the grid provided plot a graph ofI1/L(y axis − ) against L (m) (4 marks) 9. Determine the gradient of the graph. (2 marks)
gradient = Δ ¹/I (A−1) = (2.35 − 1.5) A−1  ✓½
ΔL(m)        (0.44 − 0.14)m  ✓½
= 2.833A−1m−1 OR 2.833 (Am)−1  ✓1
10. Given that the equation 1/L = P/EAL + r/E  holds for the graph, determine the value of ρ and r   (3 marks)
EA
ρ                      =  2.833(Am)−1
3.0V × 7.071 × 10−8 m2   (substitution)
ρ = 2.833 A −1m−1 × 3.0V × 7.071 × 10−8m2
ρ = 6.00964 × 10−7Ωm  ✓½ (accuracy)
r/E - y-intercept  ✓½ (equation)
r/3.0V = 1.1A−1  ✓½  (substitution)
r = 3.3 Ω   ✓½ (accuracy0

QUESTION 2

PART A

You are provided with the following:

• A lens and a lens holder.
• A screen with cross wires
• A candle
• A metre rule.
Proceed as follows:
1. Arrange the lightened candle, the lens and the screen as shown in figure 2. Adjust the position of the screen until a sharp inverted image of the candle is formed on the screen. 1. Measure the image distance v
v =  ……15.0 ± 2.0 ✓1……………………… cm (1 mark) 1 d.p a must
2. Determine the focal length of the lens using the formula
f =   uv      (2 marks)
u + v
30 × 15.0  ✓1
30 + 15.0
= 10cm  ✓1
2. Now arrange the lighted candle, the screen with cross wires and the lens as shown in figure 3. Ensure that the centre of the lens, the cross-wires, and the candle flame lie on the same horizontal line. The candle flames should be placed close to the cross-wires for better illumination. 1. Adjust the position of the lens until a sharp image of the cross-wire is formed on the screen next to the cross wires. (Hint: You have to rotate the lens slightly about a vertical axis so that the image of the cross-wires falls on the screen next to the cross wires and not on the cross-wires.)
Measure the distance d, between the lens and the screen.
d=…………5.0 ± 4.0  ✓1……………………. cm (1 mark) 1 d.p is a must
2. Determine the values of L and X:
1. L =   df      (2 marks)
f − d
L = 5.0 × 10  ✓1
10 − 5
= 10cm  ✓1
2. X =  + 1 (2 marks)
2f
X =    10cm     + 1  ✓1
2 × 10cm
x = 1.5cm  ✓1

PART B

You are provided with the following:

• A metre rule
• A knife edge
• One 50g mass and a 100 g mass
• Two pieces of threads each 30 cm long
• Some water in a beaker
• Liquid L in a beaker
• Tissue paper

Procced as follows

1. Balance the metre rule on the knife edge and record the reading at this point
Balance point = …………50.0 ± 0.5  ✓1…………………………cm mark (1 mark) 1 d.p is a must
For the rest of this experiment the knife edge must be maintained at this position.
2. Set up the apparatus as shown in the figure 4
Figure 4 The balance is obtained by adjusting the position of 100g mass when 50g mass is fully immersed in water. Record the values of X and D.
X =……………17.5 ± 0.5cm ✓1…………………………………… (1 mark)  1 d.p is a must
D =…………40.0 ± 1.0cm ✓1……………………………………… (1 mark)  1 d.p is a must
3. Using the principle of moments;
1. determine the weight W1of the 50g mass in water (2 marks)
W1 = 1 × 0.175   ✓½
0.4
= 0.4375N  ✓1
2. determine the Upthrust UW in water (1 mark)
UW = 0.5 − 0.4375  ✓½
= 0.0625 N  ✓½
4. Remove the 50 g mass from the water and dry it using a tissue paper.
Keeping D constant, adjust the position of 100g mass until the metre rule is balanced and record the value of distance X when the 50g mass is fully immersed in liquid L.
X =…………18.0 ± 0.5  ✓1………………………….. (1 mark) 1 d.p is a must
1. Determine the weight W2 of the 50g mass in liquid L. (2 marks)
W2 = 1 × 0.18  ✓1
0.4
= 0.45N  ✓1
2. Determine the Uphtrust UL in the liquid. (1 mark)
UL = 0.5 − 0.45  ✓½
= 0.05N  ✓½
5. Determine the relative density R.D of the liquid L, given that R.D = UL  (1 mark)
UW
R.D =   0.05     ✓½
0.0625
=  0.8 ✓½
6. Find the density of liquid L in S.I unit (1 mark)
ΡL = 0.8 × 1000 ✓½
= 800kg/m3 ✓½

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