Physics Paper 3 Questions and Answers - Kassu Jet Joint Exams 2020/2021

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232/3

PHYSICS

Paper 3

INSTRUCTIONS TO CANDIDATES

Write your name and index number in the spaces provided.
Mathematical tables and non-programmable calculators may be used.
This paper consists of three questions.
Attempt all the questions in the spaces provided.
ALL working MUST be clearly shown.

QUESTIONS

QUESTION ONE

Apparatus

stopwatch
250ml beaker
Rubber bun
Thermometer
Bunsen burner
Tripod
Gauze
Retort stand and clamp
Hot water

figure 1 phyp3kassu

Procedure

1. Measure and record the ambient temperature, TA =…………………..⁰C (1 mark)
2. Fill an empty beaker with exactly 150ml of hot water (check the side scale of the beaker)
3. Set up the apparatus as shown in figure 2. Ensure the thermometer is about 2cm above the bottom of the beaker.
4. Record the initial highest temperature of water TH=………………….. ⁰C (1 mark)

Start the stopwatch and time for every 2.0 minutes the temperature T of water. Record the temperature in Table below for 20 minutes

Time(t) in minutes	2	4	6	8	10	12	14	16	18	20
Temperature (T) ^oC
(T − T_A)^oC
Log₁₀ (T − T_A) 2 d.p

(6 mark)

Plot a graph of Log₁₀(T − TA) against time (Hint: Log₁₀(T − TA) should start at 1.0) (5 mark)
From the graph determine:
1. The Slope S (3marks)
2. The cooling constant , K of water given S=-0.4343K (2 mark)
Given that the specific heat capacity of water is 4.2J/g/⁰C determine the heat lost when the water cools to the temperature of the surrounding ( 2 mark)

QUESTION TWO

PART A

You are provided with the following apparatus :

One resistor labelled R = 4.0Ω
A wire labelled W mounted on milliameter scale
A wire labelled S mounted on a milliameter scale
One dry cell and a cell holder
One jockey
one centre zero galvanometer
Eight connecting wires, four with crocodile clips at both ends
A micrometer screw gauge
A switch

Proceed as follows

Determine the average diameter D, of the wire labelled W using the micrometer screws gauge provided.
D1 = ............................................................ mm (½ mark)
D2 = ............................................................. mm (½ mark)

D = D1 + D2 (in cm)
2 (1 mark)
Set up the apparatus as shown in the circuit diagram in figure 2

Use the crocodile clips to fix length L, of wire labelled S at 50cm from the end connected to the galvanometer G
Close the switch and use the jockey to touch one end of the wire W, and then the other end. The deflections on the galvanometer should be in opposite directions, if not check the circuit. Adjust the positions of the jockey along the wire W until there is no deflection in the galvanometer. Record the value of x and y.
x = ..................................................................... cm (½ mark)
y = .................................................................... cm (½ mark)
Record for other values of L in table below

L(cm) 45 40 35 30 25 30

X (cm)

Y(cm)

^y/_x (3 d.p)

(4 marks)
1. Plot a graph of ^y/_x (y-axis) against L. (5 marks)
2. Determine the slope, m of the graph. (2 marks)
3. Given that K = 100D, determine the value of K. (2 marks)

PART B

You are provided with a lens P a lens holder a white screen and half metre rule.

Procedure

Set the apparatus as shown in figure below. Focus a sharp image of a distant object on the screen (e.g window frame). The object should be 10cm away. The object should be at least 10cm away.

Measure the distance x in cm between the lens and the screen at which a sharp image is obtained repeat this two times, using different objects and record your readings in the table below

Object Distance X, (cm)

1

2

(2 marks)
Calculate the average value of x (1 mark)
What is the physical significance of the result obtained in (iii) above? (1 mark)

Marking Scheme

QUESTION ONE

Procedure

1. Measure and record the ambient temperature, TA =…………24………..⁰C (1 mark)
2. Fill an empty beaker with exactly 150ml of hot water (check the side scale of the beaker)
3. Set up the apparatus as shown in figure 1. Ensure the thermometer is about 2cm above the bottom of the beaker.
4. Record the initial highest temperature of water TH=………83………….. ⁰C (1 mark)

Start the stopwatch and time for every 2.0 minutes the temperature T of water. Record the temperature in Table 2 for 20 minutes

Time(t) in minutes	2	4	6	8	10	12	14	16	18	20
Temperature (T) ^oC	72	71	67	63	60	58	56	54	52	51
(T − T_A)^oC	48	47	43	39	36	34	32	30	28	27
Log₁₀ (T − T_A) 2 d.p	1.68	1.67	1.63	1.59	1.56	1.53	1.51	1.48	1.45	1.43

(6 mark)

Plot a graph of Log₁₀(T-TA) against time (Hint: Log10(T-TA) should start at 1.0) (5 mark)
From the graph determine:
1. The Slope S (3marks)
  G =^Δy/_Δx = ⁽^{1.65 − 1.45)}/₍_{4 − 18)}
  = − 0.01429/min
2. The cooling constant , K of water given S=-0.4343K (2 mark)
  − 0.01429 = − 0.4343 K
  K = 0.03289
Given that the specific heat capacity of water is 4.2J/g/0C determine the heat lost when the water cools to the temperature of the surrounding ( 2 mark)
H = mcΔθ
m = 150 cm³ × 1 g/cm³
= 150g
H = 0.15 × 4200 × 59
= 37, 170 J

QUESTION TWO

PART A

You are provided with the following apparatus :

One resistor labelled R = 4.0Ω
A wire labelled W mounted on milliameter scale
A wire labelled S mounted on a milliameter scale
One dry cell and a cell holder
One jockey
one centre zero galvanometer
Eight connecting wires, four with crocodile clips at both ends
A micrometer screw gauge
A switch

Proceed as follows

Determine the average diameter D, of the wire labelled W using the micrometer screws gauge provided.
D1 = ....................0.30................................... mm (½ mark)
D2 = ....................0.30................................... mm (½ mark)
D = D1 + D2 (in cm)
2
0.30 + 0.30 = 0.30 mm = 0.03 cm
2
Set up the apparatus as shown in the circuit diagram in figure below
Use the crocodile clips to fix length L, of wire labelled S at 50cm from the end connected to the galvanometer G
Close the switch and use the jockey to touch one end of the wire W, and then the other end. The deflections on the galvanometer should be in opposite directions, if not check the circuit. Adjust the positions of the jockey along the wire W until there is no deflection in the galvanometer. Record the value of x and y.
x = ............................88.3.............................. cm (½ mark)
y = ............................11.7................................. cm (½ mark)

Record for other values of L in table 3 below

L(cm)	45	40	35	30	25	30
X (cm)	92.6	93.5	94.5	95.0	96.0	96.5
Y(cm)	7.4	6.5	5.5	5.0	4.0	3.5
^y/_x (3 d.p)	0.080	0.070	0.058	0.053	0.042	0.036

(4 marks)

1. Plot a graph of ^y/_x (y-axis) against L. (5 marks)
2. Determine the slope, m of the graph. (2 marks)
  G =Δy = (8− 0) × 10⁻² = 0.08
  Δx (45 − 0) 45
  = 1.778 × 10⁻³ /cm
3. Given that K = m D2, determine the value of K. (2 marks)
  K = 100 × ^0.30/₁₀
  = 30 mm

PART B

You are provided with a lens P a lens holder a white screen and half metre rule.

Procedure

Set the apparatus as shown in figure 4 Focus a sharp image of a distant object on the screen (e.g window frame). The object should be 10cm away. The object should be at least 10cm away.
Measure the distance x in cm between the lens and the screen at which a sharp image is obtained repeat this two times, using different objects and record your readings in table 4 below

Table 4

Object Distance X, (cm)

1 10.0

2 10.0

(2 marks)
Calculate the average value of x (1 mark)
10 +10 = 10 cm
2
What is the physical significance of the result obtained in (iii) above? (1 mark)
Focal length