## Physics Paper 3 Questions and Answers - Mang'u Mock 2020 Exam

PHYSICS
PAPER 3
TIME: 2 HOURS.

Instructions to candidates

• This paper consists of TWO Sections: A and B.
•  ALL working MUST be clearly shown.
• Mathematical tables and electronic calculators may be used.

Question 1

You are provided with the following apparatus:

• micrometer screw gauge
• clamp
• boss
• stand
• optical pins
• Copper wire
• protractor
• Two pieces of plasticine
• cork

Procedure

1. Measure the diameter of the wire using the micrometer screw gauge
d=............cm. (1mk)
2. Set up the apparatus as shown in the diagram below 1. Bend the wire in the middle so as to make an angle of 40°. Attach the two small pieces of plasticine at both ends of the bend as shown in the diagram.
2. Place the bent wire on the optical pin and give a small horizontal displacement. Note the time for 10 complete oscillations and record in the table below.
3. Repeat the procedure above for other values of (8mks)
 Angle θº Time t for 10 oscillations (s) Period T (s) Frequency f(Hz)= 1/T f2(Hz)2 Cos(θ/2) 40º 60º 80º 100º 120º

1. On the graph paper provided, plot a graph of f (y-axis) against cos θ/2 (5mks)
2. Determine the gradient S of the graph(3mks)
3. The equation for the oscillation of the wire is given by the formula:
f2 = 150 z cos(θ/2)
4Π2L
Given that the length of the wire L 15cm find the value of Z. (3mks)

Question 2

You are provided with the following apparatu

• A mounted wire labeled N.
• A voltmeter
• A milliammeter
• A switch
• Two dry cells and two cell holders.
• Six connecting wire with at least two crocodile clips
• Four 1000Ω resistors labelled T.
• A diode.

Procedure

1. Set up the apparatus as shown below.
1.
1. Connect the above apparatus as shown in the circuit diagram below with the switch S open 2. With the switch S open record E the voltmeter reading (1mk)
B= ______________________
3. Close the switch and record V, the voltmeter reading and I, the ammeter reading (imk)
V= ______________________(1mk)
I= ______________________(1mk)
4. Given that: E-V=Ir. Find for the dry cell (3mks)
2. Now set the apparatus as shown in the set up below 1. Close the switch and adjust the length x by moving the jockey along the length of the wire mounted on the metre scale till the value of x is 0cm. record the values on the Milliammeter and the voltmeter; Milliammeter.......................................A (1mk)
Voltmeter............................................A(1mk)
2.  Repeat the experiment by now using x=10cm and note the readings on the milliammeter and voltmeter.
3. Repeat ii. For other values of x and fill the table below
 Distancex(cm) 0 10 20 30 40 50 60 70 80 Current I(mA) p.d (V)
6 mks
4. By using values obtained, plot a graph of current I against p.d. (5 mks)
5. Find from the graph the value of current when p.d is 0.35V. (1 mk)

MARKING SCHEME

Question 1

1. Measure the diameter of the wire using the micrometer screw gauge
d=............cm. (1mk)
2. Set up the apparatus as shown in the diagram below 1. Bend the wire in the middle so as to make an angle of 40°. Attach the two small pieces of plasticine at both ends of the bend as shown in the diagram.
2. Place the bent wire on the optical pin and give a small horizontal displacement. Note the time for 10 complete oscillations and record in the table below.
3. Repeat the procedure above for other values of (8mks)
 Angle θº Time t for 10 oscillations (s) Period T (s) Frequency f(Hz)= 1/T f2(Hz)2 Cos(θ/2) 40º 60º 80º 100º 120º

1. On the graph paper provided, plot a graph of f (y-axis) against cos θ/2 (5mks)
2. Determine the gradient S of the graph(3mks)
3. The equation for the oscillation of the wire is given by the formula:
f2 = 150 z cos(θ/2)
4Π2L
Given that the length of the wire L 15cm find the value of Z. (3mks)

Question 2

1. Set up the apparatus as shown below.
1.
1. Connect the above apparatus as shown in the circuit diagram below with the switch S open 2. With the switch S open record E the voltmeter reading (1mk)
B= ______________________
3. Close the switch and record V, the voltmeter reading and I, the ammeter reading (imk)
V= ______________________(1mk)
I= ______________________(1mk)
4. Given that: E-V=Ir. Find for the dry cell (3mks)
2. Now set the apparatus as shown in the set up below 1. Close the switch and adjust the length x by moving the jockey along the length of the wire mounted on the metre scale till the value of x is 0cm. record the values on the Milliammeter and the voltmeter; Milliammeter.......................................A (1mk)
Voltmeter............................................A(1mk)
2.  Repeat the experiment by now using x=10cm and note the readings on the milliammeter and voltmeter.
3. Repeat ii. For other values of x and fill the table below
 Distancex(cm) 0 10 20 30 40 50 60 70 80 Current I(mA) p.d (V)
6 mks
4. By using values obtained, plot a graph of current I against p.d. (5 mks)
5. Find from the graph the value of current when p.d is 0.35V. (1 mk)

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