## Physics Paper 3 Answers anad Confidential - Lanjet Joint Mock Exams 2022

### CONFIDENTIAL

INSTRUCTIONS TO SCHOOLS

1. The information contained in this paper is to enable the head of school and the teacher in charge of Physics to make adequate preparations for this Physics practical examination. NO ONE ELSE should have access to this paper or acquire knowledge of its contents. Great care MUST be taken to ensure that the information here does not reach the candidates either directly or indirect.
2. The physics teacher should note that it is his / her responsibility to ensure that each apparatus acquired for this examination agrees with the specifications given.
3. The question paper will not be opened in advance.
Each candidate will require the following;

PART A:
QUESTION 1:

1. Concave mirror of focal length 14.5cm
• Meter rule
• Candle
• Screen
2. A meter rule
2 pieces of thread approximately 30cm
A knife edge (wedge of height 25cm)
50g mass
100g mass

QUESTION B

• Ammeter ( 0 – 1.0A)
• Voltmeter ( 0 – 2.5V)
• A resistance wire PQ mounted on a mm scale (s.w.g 28mm)
• Two new dry cells
• A switch
• Cell holder
• Six connecting wires

### MARKING SCHEME

Question 1 (Curved mirror)

 U (cm-1) 15 20 25 30 35 40.6 V (cm-1) 60.5 30 23 20 15 10 1/u (cm-1) 0.0667 0.05 0.04 0.033 0.256 0.025 1/vcm-1 0.0165 0.0333 0.0435 0.0488 0.056 0.0601

Error in U ± 0.5 cm
Error in V ± 0.5 cm

f=1÷(6.875×10-2)=0.14545×102=14.5cm

PART B:(a)
RESULTS TABLE

 L(M) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 I(A) 0.5 0.44 0.4 0.38 0.36 0.32 0.3 p.d (V) 1 1.2 1.3 1.4 1.5 1.6 1.7 R = V/I (Ω) 2 2.73 3.25 3.68 4.17 5 5.67 1/IA-1 2 2.27 2.5 2.63 2.78 3.13 3.33

d) I – Values all correct values (3mks)
At 4 correct values (1mk)
V - Values all correct values (3mks)
At least 4 correct values (1mk)
Plotting graph (5mks)
-plotting 5-7 pts 2mks
4-5pts 1mk
1-3pts no mk
-straight line 1mk
-scale appropriate 1mk
-axes labelled 1mk

e) A (14.5 , 5 ) B(32.5 , 53.5 ) (1mk)
evaluation (1mk)
= 2.69 A accuracy ( ½ )
Unit ( ½ )
f) i) R
E = K = Slope = 2.69V (1 mk)
R =
ii) -r = -35 10-1 = 3.5 Realizing y = y intercept (1mk)

B: (b)

 d1(CM) 30 26 24 22 18 16 d2(CM) 59 41.8 34.8 28.1 13.6 6.3 F1d1(NM) 0.3 0.26 0.24 0.22 0.18 0.16 F2d2(NM) 0.295 0.209 0.174 0.141 0.065 0.035

Each x 1∕2 =3mks
Any 5 correct readings x1∕2=2.5mks
-2.5mks
Error d2=+ or _ 0.1
G=50CM. mark
F1=1N
F2=0.5N

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