Physics Paper 3 Questions and Answers - Form 3 Term 3 Opener Exams 2021

INSTRUCTIONS TO CANDIDATES

QUESTIONS

Question 1
You are provided with the following apparatus
- Ammeter
- A voltmeter
- A wire mounted on a millimeter scale
- A switch
- A new dry cell
- A micrometer screw gauge
- Connecting wires
- A jockey

Proceed as follows:

Measure the diameter d of the mounted wire at three different points
d₁= ____________________________________ mm
d₂=____________________________________ mm (½mk)
d₃=____________________________________ mm
Average d = ____________________________ mm (½mk)
Set up the apparatus as shown in the circuit diagram.

Close the switch and tap the mounted wire with jockey as shown in the circuit. Ensure that both meters show positive deflection, open the switch.
Tap the wire at L= 20cm, close the switch, read and record in the table the ammeter and voltmeter reading.
Repeat the procedure in (c) for other values of L shown in the table and complete the table.(6mks)

L(m) V(Volts) I(A) R = ^V/_I

0.2

0.3

0.4

0.5

0.6

0.7

0.8
Plot a graph of R against L(m). (5mks)
Determine the slope of the graph. (3mks)
Given that R= p^L/_A where A is the cross-sectional area of the wire and p is a constant for the material of the wire, determine the value of the constant p. (3mks)

Part I
You are provided with the following;

Part II

You are provided with a glass block, 4 optical pins, a soft board, one plain paper.

Place the rectangular glass block on a sheet of paper fixed on the soft board with one of its longest face uppermost. Mark the outline ABCD as shown in the figure. Remove the glass block and draw a line EF to represent a ray of light making an angle of incidence i=30º with the longest side BC of the block.
Stand pins p1and p2 on this line as far as possible. Replace the block and mark the emergent ray by looking into the side AD of the block and placing pins p3 and p4 in line with images of p1 and p2 as seen through the glass block. Remove the block and the pins and draw ray EFGH as shown in the figure below.
1. Draw the normal at G as shown.
2. Measure angle B (1mk)
  B = ……………………………………………………………
3. Given that k = sin 30º
  sin B
  Calculate the value of k. (2mks)
4. The main paper used should be handed over together with this paper (correct use made of the plain paper)(1mk)

Question 1

table

L(m)	V(Volts)	I(A)	R = ^V/_I
0.2	0.30	0.10	All correct To four significant or exact (2mks)
0.3	0.40	0.10
0.4	0.50	0.10
0.5	0.60	0.10
0.6	0.70	0.10
0.7	0.90	0.10
0.8	1.00	0.10
	±0.05 (2mks)	±0.05 (2mks)

- axes labeled with units (1mk)
- Uniform and simple scale (1mk)
- correct plotting within one small square (4pts x ½mk = 2mks)
- Straight line with a positive gradient passing at least three points. (1mk)
- Correct interval within one small square (1mk)
- Correct substitution and evaluation (1mk)
- Answer accuracy with units (1mk)
- Slope = ^P/_A area to be in SI unit.
- Correct calculation of cross sectional area of the wire, A = π (^d/₂)² (1mk)
- P= slope × A; correct substitution and evaluation. (1mk)
- Answer accuracy with unit. (1mk)

Part 1

Table

- Axes labeled with units (1mk)
- Uniform and simple scale (1mk)
- Correct plotting within one small square (4pts x ½mk = 2mks)
- Straight line with a positive gradient passing through at least 3 points. (1mk)
- Correct interval within one small square. (½mk)
- Correct substitution and evaluation (½mk)
- Answer accuracy with units (1mk)
- Form y= mx + c
  Slope = 4π²
  k
- Correct substitution (1mk)
- Correct evaluation (1mk)
- Answer accuracy with units (1mk)