## Physics Paper 3 Questions and Answers with Confidentials - MECS Cluster Joint Pre Mock Exams 2021/2022

PHYSICS
PAPER 3: PRACTICAL

QUESTION 1 (20 marks)
You are provided with the following

• A rectangular glass block.
• Four optical pins.
• Soft board.
• A plain paper.
• 4 thumb tacks.

Proceed as follows:

• Place the glass block on the plain paper and trace it out using a pencil. • Remove the glass block and construct a normal at B (a third of the outline from left edge) towards the edge as shown in the set up above.
• Construct an incident ray AB of an angle of incidence i equal to 15Â°. Fix two optical pins P1 and P2 along ray AB.
• Replace the glass block and trace the ray ABCD by locating Positions of P3 and P4 on the opposite side of the glass block such that P1, P2, P3 and P4 appear to lie on a straight line.
• Remove the glass block and draw the path of the ray ABCD using pencil.
• Measure length L (B to C) using a ruler and record it on the table below

1. Complete the table below for the values i = 25Â°,35Â°,45Â° and 55Â°.
 iÂº L(cm) L2(cm2) 1/LÂ²(cm-2) Sin i Sin2i 15 25 35 45 55
(8mks)
2. Plot a graph of 1/LÂ²(y â axis) against Sin2 i (5mks)
3.
1. Determine slope S, from the graph (3mks)
2. the intercept C, of the 1/L axis (1mk)
3. Given that C= Sn2, determine the value of constant n (Use the absolute value of S). (3mks)

QUESTION 2 (20 marks)

PART A
You are provided with;

• A cell and a cell holder
• A resistance wire on millimeter scale
• Six connecting wires with crocodile clips eac
• An Ammeter (0 â 1 A)
• A voltmeter (0 - 3 V)
• A micrometer screw gauge
• A switch 1.
1. Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
d1=
d2=
2. Calculate the average diameter d, in metres. (2mks)
2. Connect the cell, the ammeter and the 1.0 m length of resistance wire PQ in series.

1. Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
Vo = â¦â¦â¦â¦..
Io = â¦â¦â¦â¦â¦
2. Calculate the resistance of the wire Ro. (1mks)
Ro =
3. Calculate the cross-section area of the wire. (1mk)
A =Ï(d/2)2
4. Determine the value of quantity Ï of the wire given the relation Ï=(R_o A)/L where L is length of the wire PQ. (2mks)

PART B

Apparatus

• A metre rule
• One 50 g mass and one 100 g mass
• A stand with bosses
• Some water in a beaker
• Liquid L in a beaker, tissue paper

Procedure

1. Balance the metre rule on the knife edge and record the reading at this point.
Balancing Point = â¦â¦â¦â¦â¦â¦. (1mk)
(For the rest of the experiment the ruler must be balanced at this point)
2. Set the apparatus as shown in the figure below. Use the thread provided to hang the masses such that the positions of support can be adjusted. 3. The balance is attained by adjusting the position of the 100 g mass. Note that the distance x and D are measured when the 50 g mass is fully submerged in water. Record X and D
X = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... cm. (1mk)
D = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... cm. (1mk)
4. Applying the principle of moments, determine the weight W1 of the 50 g mass in water and hence determine the upthrust Uw in water
W1 = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.â¦N. (2mks)
Uw =â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ N. (1mk)
5. Remove the 50 g mass from the water and dry it using the tissue paper. Balance the metre rule when the mass of 50 g is fully submerged in the liquid L while maintaining distance D. Record the value of the distance X.
X = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. cm. (1mk)
6. Apply the principle of moments to determine the weight W2 of the 50 g mass in the liquid L and hence determine the upthrust UL in the liquid.
W2 = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. N. (1mk)
UL = â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ N. (1mk)
7. Determine the relative density R.D of the liquid, given that (1mks)
R.D=UL/UW

CONFIDENTIAL

QUESTION 1

• A rectangular glass block.
• Four optical pins.
• Soft board.
• A plain paper.
• 4 thumb tacks.
• Ruler and protractor

QUESTION 2

• A metre rule.
• One 50 g mass and one 100 g mass
• A stand with bosses
• 90 cm3 of water in a 100 ml beaker
• 90 cm3 of paraffin labelled liquid L in a 100ml beaker
• Tissue paper
• A cell and a cell holder
• A resistance wire on millimeter scale
• Six connecting wires with crocodile clips each
• An Ammeter (0 â 1 A)
• A voltmeter (0 - 3 V)
• A micrometer screw gauge
• A switch

MARKING SCHEME

QUESTION 1 (20 marks)
You are provided with the following

• A rectangular glass block.
• Four optical pins.
• Soft board.
• A plain paper.
• 4 thumb tacks.

Proceed as follows:

• Place the glass block on the plain paper and trace it out using a pencil. • Remove the glass block and construct a normal at B (a third of the outline from left edge) towards the edge as shown in the set up above.
• Construct an incident ray AB of an angle of incidence i equal to 15Â°. Fix two optical pins P1 and P2 along ray AB.
• Replace the glass block and trace the ray ABCD by locating Positions of P3 and P4 on the opposite side of the glass block such that P1, P2, P3 and P4 appear to lie on a straight line.
• Remove the glass block and draw the path of the ray ABCD using pencil.
• Measure length L (B to C) using a ruler and record it on the table below

1. Complete the table below for the values i = 25Â°,35Â°,45Â° and 55Â°.
 iÂº L(cm) L2(cm2) 1/LÂ²(cm-2) Sin i Sin2i 15 6.5 42.25 0.02367 0.2588 0.06698 25 6.6 43.56 0.0230 0.4226 0.1786 35 6.9 47.61 0.02100 0.5736 0.3290 45 7.3 53.29 0.01877 0.7071 0.5 55 7.7 59.29 0.01687 0.8192 0.6710 - All values to 1dp-Each correct value(1mk up to max of 4points(max 4mks) Correct conversion to4sf or exact of allvalues=1mk Correct conversion to4sf or exact of allvalue= 1mk Correct conversionto 4sf or exact forall values=1mk Correct conversionto 4sf or exact forall values = 1mk
(8mks)
2. Plot a graph of 1/LÂ²(y â axis) against Sin2 i (5mks)
3.
1. Determine slope S, from the graph (3mks)

S=(â1/LÂ² )/âSin2i

=0.024-0.016cm-2
0.1-0.75

=0.008 cm-2
-0.65

=-0.012308 cm-2

2. the intercept C, of the 1/L axis (1mk)

C=-0.012308 cm-2

3. Given that C= Sn2, determine the value of constant n (Use the absolute value of S). (3mks)

n2    0.0252 cm-2
0.012308 cm-2
=2.0475
n=1.4309 QUESTION 2 (20 marks)

PART A
You are provided with;

• A cell and a cell holder
• A resistance wire on millimeter scale
• Six connecting wires with crocodile clips eac
• An Ammeter (0 â 1 A)
• A voltmeter (0 - 3 V)
• A micrometer screw gauge
• A switch
1.
1. Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
d1=   0.29 mm (+ or â 0.02 mm)
d2=  0.31 mm (+ or â 0.02 mm)

2. Calculate the average diameter d, in metres. (2mks)

d=d1+d2
2
=0.29+0.31     =0.30 mm
2
=      0.30       =0.00030 m
1000

2. Connect the cell, the ammeter and the 1.0 m length of resistance wire PQ in series.

1. Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
Vo =    0.81 V    (+ or â 0.1 V)
Io =  0.1 A        (+ or â 0.02 A)

2. Calculate the resistance of the wire Ro. (1mks)
Ro = =0.81 V/0.1 A

3. Calculate the cross-section area of the wire. (1mk)
A =Ï(d/2)2
A  =Ï0.00032
2
=7.069 Ã10-8   m2
4. Determine the value of quantity Ï of the wire given the relation Ï=RoA/L where L is length of the wire PQ. (2mks)

Ï =8.1 Î© Ã7.069 Ã10-8   m2
1 m
Ï =5.726 Ã10-7

PART B

Apparatus

• A metre rule
• One 50 g mass and one 100 g mass
• A stand with bosses
• Some water in a beaker
• Liquid L in a beaker, tissue paper

Procedure

1. Balance the metre rule on the knife edge and record the reading at this point.
Balancing Point = 50.2 cm (+ or -1 cm)  (1mk)

(For the rest of the experiment the ruler must be balanced at this point)
2. Set the apparatus as shown in the figure below. Use the thread provided to hang the masses such that the positions of support can be adjusted. 3. The balance is attained by adjusting the position of the 100 g mass. Note that the distance x and D are measured when the 50 g mass is fully submerged in water. Record X and D
X = 18.0 cm. (1mk)
D = 40.2 cm. (1mk)
4. Applying the principle of moments, determine the weight W1 of the 50 g mass in water and hence determine the upthrust Uw in water
W1 =

sum of clockwise moments=sum of anticlockwise moments
40.2     Ã  W1 =     18     Ã 1
100                    100
W1=18/100 Ã 1 Ã 100/40.2
W1=0.4478 N

Uw =

Uw=Real weight-Apparent weight
Uw=0.5 N-0.4478 N
=0.0522 N

5. Remove the 50 g mass from the water and dry it using the tissue paper. Balance the metre rule when the mass of 50 g is fully submerged in the liquid L while maintaining distance D. Record the value of the distance X.
X =

X  =  68.8 â 50.2

= 18.4 cm.
6. Apply the principle of moments to determine the weight W2 of the 50 g mass in the liquid L and hence determine the upthrust UL in the liquid.
W2

sum of clockwise moments=sum of anticlockwise moments

40.2/100 Ã W2 = 18.4/100 Ã 1
W2=18.4/100 Ã 1 Ã 100/40.2
W2=0.4577 N

UL

Uw=0.5 N-0.4577 N
=0.0423 N

7. Determine the relative density R.D of the liquid, given that (1mks)
R.D=UL/UW
=0.0423/0.0522

=0.8103