## Physics Paper 3 Questions and Answers with Confidentials - Mokasa II Mock Examination 2021/2022

PHYSICS
Paper 3
PRACTICAL

Instructions to Candidates

• Answer ALL the questions in the spaces provided.
• Mathematical tables and electronic calculator may be used.
• Candidates should answer the questions in English. ## Questions

QUESTION 1
You are provided with the following apparatus

• Two dry cells
• Nichrome wire mounted on the meter rule
• An ammeter
• Cell holder
• Voltmeter
• 8 connecting wires
• Switch
• A jockey

Proceed as follows.

1. Determine the electromotive force of the dry cells.
E =…………………………………….. (1 mark)
2. Draw a diagram to show how the e.m.f,E of the dry cells is measured. ( 1 mark)
3. Connect the circuit as shown below Connect the ends of A and C where AC is 100 cm across the terminals as shown above. Close the switch and record both ammeter reading and the voltmeter reading.
Current I = …………………………… ( 1 mark)
P.d (V) =………………………………. ( 1 mark)
4. Proceed for the lengths shown in the table and record the corresponding values of current,I and voltage,V ( 6marks)
 Length L(cm) 100 70 60 50 40 20 I(A) P.d(V)
5. Plot a graph of p.d,V(V) against current,I(A) (5 marks)
6. Determine the slope of the graph. (3 marks)
7. Given that E = V+Ir, determine the following using the graph above.
1. Internal resistance r (1mk)
2. The e.m.f E of the dry cells (1mk)

Question 2

PART A
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

Proceed 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 below The balance is obtained by adjusting the position of 100g mass when 50 g 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.
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=  U (2marks)
UW
6. Find the density of liquid X in S.I unit (2marks)

PART B
You are provided with the following:

• A semi-circular glass block
• Soft board
• White paper
• Four Optical pins
• Two Thumb pins
• Vernier calipers

Procedure

1. Measure the thickness of the glass block using the Vernier calipers provided
t = ________cm __________m (1mk) 2. Fix the plain paper to the soft board using drawing/thumb pins
3. Place the semi-circular glass block on the paper and trace its outline. Remove the block and label A and B as shown in figure above.
4. Identify the centre O of the plane and draw the normal at that point as shown in the figure above.
5. Measure incident angle i as 480 then draw the incident ray
6. Place two pins P1 and P2 on the incident ray as shown.
7. Move your eyes at curved face and locate the images of pins P1 and P2, place pins P3 and P4 such that the four pins are aligned in a straight line.
8. Remove the glass block and join points P3 and P4 to meet the interface AB.
9. Measure the angle Y between incident ray and the reflected ray.
Y= ___________ (2 marks)
1. Find the value of M given that (3marks)
M = (tY/2)-1
2. Hand in the white paper used (1mark) ## Confidential

Question 1:

• Two dry cells and a cell holder
• An ammeter
• A voltmeter
• Metre rule mounted with a nichrome wire( 28 gauge)
• A switch
• 8 connecting wires

Question 2

• Metre rule
• A knife edge
• 50g mass and a 100g mass
• Two pieces of threads each 30 cm long
• 100 ml of Water in a beaker
• 100 ml of glycerine(Liquid L) in a beaker
• Tissue paper
• 4 optical Pins
• semi-circular glass block
• two thumb pins
• soft board
• plain papers
• Vernier calipers ## Marking Scheme

QUESTION 1

1. E= 3.0V  ± 0.1
2. 3. Current I = 0.12A  ± 0.05
P.d(V) = 2.60V ± 0.10
4.
 Length L(cm) 100 70 60 50 40 20 I(A) 0.12 0.16 0.18 0.2 0.24 0.36 P.d(V) 2.6 2.45 2.4 2.2 2.1 1.75
5. 6.   Slope = ΔV(v)
ΔI(A)
=  3.0 - 2.2
0 - 0.225
Slope =   - 0.8
0.225
= -3.5556 Ohms
7.
1. V= -Vi + E
y= mx + c
M= -r but
r = 3.5556Ω

2. e.m f , E= 3.0V
( accept students Y- intercept)
- Confirm from the graph

QUESTION 2

PART A

1. Balance point = 50.0 ± 0.5 cm mark

2. X= 17.5 ± 0.5cm
D= 39.8 ± 0.5cm

3.
1. F1d1 = F2d2
W139.8/100 = 0.1 x 17.5/100
W1 = 0.0175
0.398
W1 = 0.04396N

2. Uw = WA - W1
=0.5 - 0.04396
= 0.456N

4.  X = 17.0 ± 0.5cm
1. F1d1 = F2d2
W2 x 39.8/100 = 0.1 x 17.0/100
W2 = 0.04271N

2. UL = WA -WL = 0.5 0.04271
= 0.45729N
5. R.D = 0.45729 = 1.002829
0.456
6.

PART B

1. T = 1.50CM 0.015M
2. ...
3.   ...
4. ...
5. ...
6. ...
7. y= 96° ± 2°
1. M = (0.015/2 x 96)-1 = 1.388
≈ 1.4
2. Check the plain paper to confrim what the student has drawn

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