## Physics Paper 3 Questions and Answers - Mangu High School Mock Exams 2022

### QUESTIONS

QUESTION 1 (20 MARKS)

1. You are provided with the following:
• A galvanometer
• A dry cell and a cell holder
• A switch
• A wire labelled Y mounted on a piece of wood.
• Eight connecting wires each with a crocodile clip at one end.
• A resistance wire labelled AB mounted on a millimeter scale.
• Six 10 Ohm carbon resistors
• A jockey or crocodile clip
• Micrometer screw gauge (to be shared)

Proceed as follows:

1. Set up the circuit as shown in figure 1 below, with X being one of the 10 ohms carbon Figure 1
2. Close the switch. Tap the jockey at various points on the wire AB and locate point P at which the galvanometer shows zero deflection, measure and record in table below the length, I where L = PB.
3. Repeat the procedure in (b) using X as two 10Ω resistors, three resistors, four resistors, five resistors and six resistors. X is the effective resistance for the parallel combination i.e. X = 10/n where n is the number of resistors in parallel.
Table 1
 Number of 10Ω carbon resistor One Two Three Four Five Six X (Ω) L (cm) 1/x (Ω-1) 1/L (cm-1)
5. Plot a graph of 1/L (y-axis) against 1/X (5 marks)
6. Determine the slope m of the graph. (2 marks)
7. Given that 1/L = R/KX + 1/K where K = 100cm. Use the graph to determine R. (2 marks)
8. Measure the diameter d and the length L of wire Y. (2 marks)
L = .............................m                 d = ................................m
9. Determine the cross-sectional area A of the wire Y. (1 mark)
A= .........................................m2
10. Determine the resistivity p of the wire Y given that its Resistance, R =pL/A (2 marks)

QUESTION 2 (20 MARKS)
PART A
You are provided with the following:

• A metre rule
• A stand, boss and clamp
• A piece of string
• A 20g mass
• A 50g mass
• A measuring cylinder containing water
• A concave mirror
• A screen
• A candle
• A mirror holder (Lens holder)

1. Using a string, suspend the metro rule on the stand so that it balances horizontally at its center of gravity. Record the centimetre mark at which the metre rule balances.
Centimetre mark ..................................... cm (1 mark)
2. With the motre rule balanced at its centre of gravity, suspend a 20 g mass at a distance of 30cm from the centre of gravity. Suspend the 50g mass on the other side of the centre of gravity and adjust its position until the rule is balanced. See figure 3. Record the distance d of the 50 g mass from the centre of gravity,
d= .............................cm
d= ..............................m           (1mk)
3.
1. Record the volume of the water in the measuring cylinder provided.
V= ...................................
2. Immerse the 20g mass fully into the water and adjust the position of the 50 g mass so that the rule balances horizontally. Record the volume V1 of the water plus 20 g mass and the distance di of the 50 g mass from the centre of gravity.
V1 =........................................... (1mk)
d1 = ..........................................cm (1mk)
3.
1. Determine the volume of the water displaced (1mk)
2. Determine the weight of the water displaced. (density of water 1g/cm3)
4.
1. Use the Principle of moments to determine the apparent weight of the 20 g mass when fully immersed in water. (g = 10N/kg) (2mks)
2. Calculate the weight of the 20 g mass in air. (g = 10N/kg) (1mk)
3. Determine the apparent loss in weight of the 20 g mass. (1mk)
PART B
5. Light the candle and place it at distance u=20 cm in front of the concave mirror. Adjust the position of the screen until a sharp image of the candle flame is obtained. See Figure below. 1. Read and record the distance v between the screen and the mirror.
v = ........................................................ (1mk)
2. Determine:
1. The magnification m of the mirror (1mk)
2. The value fi given that F1 = mu/m + 1
6. Repeat part e) for distance u¡ -18cm
1. Read and record the distance vi between the screen and the mirror.
v1 = ........................................................ (1mk)
2. determine the magnification my of the mirror (1mk)
3. Hence determine f2
7. Determine the average value of f. (1mk)

### MARKING SCHEME

QUESTION 1 (20 MARKS)

1. You are provided with the following:
• A galvanometer
• A dry cell and a cell holder
• A switch
• A wire labelled Y mounted on a piece of wood.
• Eight connecting wires each with a crocodile clip at one end.
• A resistance wire labelled AB mounted on a millimeter scale.
• Six 10 Ohm carbon resistors
• A jockey or crocodile clip
• Micrometer screw gauge (to be shared)

Proceed as follows:

1. Set up the circuit as shown in figure 1 below, with X being one of the 10 ohms carbon Figure 1
2. Close the switch. Tap the jockey at various points on the wire AB and locate point P at which the galvanometer shows zero deflection, measure and record in table below the length, I where L = PB.
3. Repeat the procedure in (b) using X as two 10Ω resistors, three resistors, four resistors, five resistors and six resistors. X is the effective resistance for the parallel combination i.e. X = 10/n where n is the number of resistors in parallel.
Table 1
 Number of 10Ω carbon resistor One Two Three (4 s.f) Four Five Six (4 s.f) X (Ω) 10 5 3.3333 2.5 2 1.666 L (cm) ± 0.5 59.0 40.7 31.5 25.4 21.4 18.8 1/x (Ω-1) 0.1 0.2 0.3 0.4 0.5 0.6 1/L (cm-1) 0.01695 0.02457 0.03174 0.03937 0.04673 0.05379
5. Plot a graph of 1/L (y-axis) against 1/X (5 marks)
If line is curve or negative gradient don't award for line
6. Determine the slope m of the graph. (2 marks)
m = Δ1/L = 0.039 - 0.0245
Δ1/X =     0.4 - 0.2
= 0.0145 = 0.0725 π/cm
0.2
If line is wrong in (e) deny gradient mark
7. Given that 1/L = R/KX + 1/K where K = 100cm. Use the graph to determine R. (2 marks)
0.0725 = R/100 = 7.25 - Ω
8. Measure the diameter d and the length L of wire Y. (2 marks)
L = ........0.300 ± 0.01.....................m                 d = ....2.3 x 10-4.m 2.1 - 2.6 x 10-4
9. Determine the cross-sectional area A of the wire Y. (1 mark)
A= .........................................m2
A = πr2
=22/7 x  (2.3 x 10-4)2
2
= 4.156 x 10-8 m2
10. Determine the resistivity p of the wire Y given that its Resistance, R =pL/A (2 marks)
R = PL
A
L = 9.975 x 10-7Ωm
7.25 = L x 0.3
4.156 x 10-8

QUESTION 2 (20 MARKS)
PART A
You are provided with the following:

• A metre rule
• A stand, boss and clamp
• A piece of string
• A 20g mass
• A 50g mass
• A measuring cylinder containing water
• A concave mirror
• A screen
• A candle
• A mirror holder (Lens holder)

1. Using a string, suspend the metro rule on the stand so that it balances horizontally at its center of gravity. Record the centimetre mark at which the metre rule balances.
Centimetre mark ..50.0.. cm (1 mark) 57 - 53.0 cm  1dp
2. With the motre rule balanced at its centre of gravity, suspend a 20 g mass at a distance of 30cm from the centre of gravity. Suspend the 50g mass on the other side of the centre of gravity and adjust its position until the rule is balanced. See figure 3. Record the distance d of the 50 g mass from the centre of gravity,
d= ......15.0.......cm ± 1 cm     1 dp
d= ....0.150......m    3 dp      (1mk)
3.
1. Record the volume of the water in the measuring cylinder provided.
V= ...17 cm3
15 - 20cm3          Accept ml
2. Immerse the 20g mass fully into the water and adjust the position of the 50 g mass so that the rule balances horizontally. Record the volume V1 of the water plus 20 g mass and the distance di of the 50 g mass from the centre of gravity.
V1 =....20cm3..... (1mk) 17.5 - 22.5cm3
d1 = ...13.0......cm (1mk) 11.0 - 15.0 cm
3.
1. Determine the volume of the water displaced (1mk)
20 - 17 = 3cm3  volume = V1 - V
2. Determine the weight of the water displaced. (density of water 1g/cm3)
convenience of volume to mass ie m = ve
must be shown
convert mass to newtons (kg to N)
4.
1. Use the Principle of moments to determine the apparent weight of the 20 g mass when fully immersed in water. (g = 10N/kg) (2mks)
principle of moments substituted
4 s.f or exact
2. Calculate the weight of the 20 g mass in air. (g = 10N/kg) (1mk)
20/1000 x 10 = 0.2N
No units
1/2 mk
Ans from correct working
3. Determine the apparent loss in weight of the 20 g mass. (1mk)
wt in air - wt in water or wt of H20) displaced
Ans from correct working
No units 1/2 mk

PART B
5. Light the candle and place it at distance u=20 cm in front of the concave mirror. Adjust the position of the screen until a sharp image of the candle flame is obtained. See Figure below. 1. Read and record the distance v between the screen and the mirror.
v = ..18.0 - 22.0 cm.. (1mk)
2. Determine:
1. The magnification m of the mirror (1mk)
m = v/u
2. The value fi given that F1 = mu/m + 1
substitution
6. Repeat part e) for distance u¡ -18cm
1. Read and record the distance vi between the screen and the mirror.
v1 = ...20.5 - 24.5... (1mk)
2. determine the magnification my of the mirror (1mk)
3. Hence determine f2
Answer from correct working no units
1/2 mks
7. Determine the average value of f. (1mk)
no units
1/2 mk

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