Physics Paper 3 Questions and Answers with Confidentials - 2021 KCSE Eldoret Diocese Mock Exams

Questions

INSTRUCTIONS TO CANDIDATES

Mathematical tables and non-programmable calculators may be used.
This paper consists of section A and section B.
ALL working MUST be clearly shown.

Question 1

You are provided with the following apparatus:

2 size D dry cells
100cm nichrome wire on a mm scale, labelled P at one end.
A bulb (2.5V) and a bulb holder.
8 connecting wires (at least 4 with crocodile clips)
Cell holder
A voltmeter (0-5V)

An ammeter (0-1A)
A jockey

Connect the apparatus provided as shown in the diagram.
Place the jockey at L = 20cm from P, then close the switch.
Record the ammeter reading and the voltmeter reading in the table below.

Repeat the experiment by placing the jockey at L = 30, 40, 50, 60 and 80cm from P.
Record your readings and complete the table below.

Length l (cm)	I (A)	Pd, V(V)	I(mA)	Pd, v(MV)	log I	log V
20
30
40
50
60
80
	3mks	3mks	-½mk	-½mk	-½mk	-½mk

Plot a graph of log I (y-axis) against log V (5mks)
Determine the slope of the graph. (3mks)
Give that log I = nlog V + log K where n and k are constants of the lamp. Determine using your graph the value of:
1. K (2mks)
2. n (2mks)

Question 2

Part A
You are provided with the following:

A retort stand, boss and clamp.
2 boiling tubes
A thermometer
Some distilled water in a beaker labelled W
Some liquid in a beaker, labelled L
A 250ml beaker containing some water.
A measuring cylinder
A stop watch
A tripod stand and wire gauze
A card board with a hole in the middle
A burner.

Proceed as follows
1. Clamp one boiling tube on the retort stand. Measure and pour 45ml, of the distilled water, W
  into a boiling tube. Set up the apparatus as shown in the figure below.
2. Heat the water in the large beaker (250ml) until the temperature of the distilled water reached 850C. Remove the boiling tube from the hot water by lifting up the retort stand and placing it away from the burner.
3. Stir the water in the boiling tube using the thermometer. Record in the table below the temperature of the distilled water at intervals of 30 seconds starting at 800C until it drops to 600C (stir the distilled water before taking any reading).
  
  Time in minutes 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
  
  Temperature of W(⁰C)
  
  Temperature of L(⁰C)
  
  Time in minutes 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5
  
  Temperature of W(⁰C)
  
  Temperature of L(⁰C)
  
  (4mks)
4. Using the second boiling tube, repeat the procedure in b and c using 45ml of liquid L instead of distilled water. Record your results in the same table.
5. Using the same axis on the grid provided, plot a graph of temperature (y-axis) against time for
  1. Distilled water, W
  2. Liquid L
    (Label the graphs of L and W. (7mks)
6. From the graph, determine:
  1. the time, t taken for the distilled water to cool from 750C to 650C.
    tw = _____________ minutes (1mk)
  2. the time, t taken for liquid L, to cool from 750C to 650C
    tL= _____________ minutes (1mk)
7. Determine the constant r given that where d, density of liquid, L = 0.8g/cm3. (2mks)

PART B
You are provided with the following:

Copper wire of length 130cm.
Test tube of diameter 1.5cm (ordinary)
Metre rule.

Procedure

By using the wire provided, make 20 closely packed turns around the said ordinary test tube as shown.

Measure the length x = ______ cm (1mk)
Use the result “X” to determine the thickness of the wire, d = ______ cm. (1mk)
Given that the volume of the wire 1/4πd²L, determine the volume, V of the wire if
L = 120cm. (3mks)

Confidential

- 2 size D dry cells.
- 100cm nichrome wire on a mm scale, labelled P at one end, 0 cm mark.
- A bulb (2.5V) and a bulb holder.
- 8 connecting wires (at least 4 with crocodile clips).
- Cell holder
- A switch
- A volt Meter ( 0 – 5V)
- An ammeter ( 0 – 1A)
- A jockey

Section B

A liquid labelled L (50 ml of paraffin).
A measuring cylinder (50ml or 100ml).
2 boiling tubes.
A thermometer.
50ml of distilled water in a beaker labelled W.
A 250ml beaker containing some water.
A stop watch
A tripoid stand and wire gauze
Clamp and stand
A card board with a hold at the middle (3cm by 3cm)
Copper wire of length 130cm. (0.28mm)
Test tube of diameter 1.5cm (ordinally)
Metre rule

Marking Scheme

Question 1

Length l (cm)	I (A)	Pd, V(V)	I(mA)	Pd, v(MV)	log I	log V
20	0.14	0.25	140	250	2.146	2.398
30	0.16	0.35	160	350	2.204	2.544
40	0.18	0.50	180	500	2.255	2.699
50	0.19	0.65	190	650	2.279	2.813
60	0.20	0.85	200	850	2.301	2.929
80	0.24	1.30	240	1300	2.380	3.114
	3mks	3mks	-½mk	-½mk	-½mk	-½mk

I(A) = x ± 0.2A ; 2dp (4sf) (4sf)
V(v) = x ± 0.10V ; 2dp

Graph attached
slope = Δ log I (from graph not the table)
Δ log V
(238 – 214) x 10^-2 Correct substitution – (1 mk)
(310 – 240) x 10^-2 Correct evaluation – (1 mk)
= 0.3429 (4 sf) ans to 4 sf or exact – (1 mk)
log I = n log v + log k
y = mx + C
1. log k = y intercept
  log k = 211 x 10-2 = 2.11 (1mk)
  k = 128.82 (4sf or exact)
2. n
  n = slope
  n = answer in e
  = 0.3429 ( exact as in e)

Question 2

PART A

Time in minutes	0	0.5	1.0	1.5	2.0	2.5	3.0	3.5	4.0	4.5
Temperature of W(⁰C)	80.0	79.0	77.5	76.0	75.0	74.0	72.5	71.0	70.0	69.0
Temperature of L(⁰C)	80.0	76.0	75.0	72.0	70.0	68.0	66.0	64.5	62.5	61.0

Time in minutes	5.0	5.5	6.0	6.5	7.0	7.5	8.0	8.5	9.0	9.5
Temperature of W(⁰C)	68.0	67.0	66.0	65.0	64.5	62.5	62.0	61.5	61.0	60.0
Temperature of L(⁰C)

Temp (0C) + 2.00C (4mks)

Graph (as attached)
1. tw = 6.5 – 2.0
  = 4.5 minutes
  Correct readings from graph – 1mk
2. tl = 2.0 – 0.6
  = 1.4 minutes
  Correct readings from the graph – 1mk
r = 4.2tl
dtw
4.2 x 1.4 = 1.6333
0.8 x 4.5
Correct substitution of tl , tw and d – 1mk
Correct evaluation of 4 SF or exact - 1mk

Part B

Length, x = 0.8 + 0.2cm - 1mk
thickness d = x
20
0.8cm = 0.04cm
20
Correct substitution of x – 1/2mk
Correct evaluation to 2 dp or exact – 1/2mk
V = 1/4 πd² L
= 1/4 x 3.142 x(0.04)² x 120
= 0.1508cm³ 1
Correct substitution of  = 3.142 , d² , L – 1mk
Correct evaluation to 4 s.f or exact – 1mk
Correct unit – 1mk