Physics Paper 3 Form 3 End Term 2 Exams 2021 with Marking Schemes
INSTRUCTIONS TO CANDIDATES
 Answer ALL the questions in the spaces provided in the question paper.
 You are supposed to spend the first 15 minutes of the 2^{1}/_{4} hours allowed for this paper reading the whole paper carefully before commencing your work.
 Marks are given for clear record of observations made, their suitability, accuracy and the use made of them.
 Candidates are advised to record their observations as soon as they are made.
 Nonprogrammable silent electronic calculators and KNEC mathematical table may be used.
PART A
 You are provided with the following:
 A retort stand, clamp and boss.
 A spiral spring.
 A stop watch.
 Three 100g masses.
 Three 50g masses.
PROCEDURE
 Suspend a 100g mass at the end of a spiral spring as shown below.
 Now give the mass a small vertical displacement and release so that it performs vertical oscillation.
 Time for 20 oscillations and determine the period.
Enter the result in the table below.  Repeat the experiment for other values of mass given and complete the table.
6marksMass (mg) 100 150 200 250 300 350 Time for 20 oscillations Period time T (s) T^{2}(S^{2})  Plot a graph of T² (S²) (y –axis) against m (kg). (5marks)
 Determine the slope of the graph. (2marks)
 Given that T^{2}=π^{2} m where k is the spring constant , use the graph to obtain the value of the spring constant k. (2marks)
PART B
You are provided with the following
 5 optical pins
 A rectangular glass block
 A plain paper
 A soft board
 4 thumb pins
Proceed as follows
 Fix the white piece of paper on the soft board using thumb pins. Place the glass block on the white paper and draw the outline of the block.
 Remove the glass block and indicate the sides A, B, C and D as shown.
 On side BC, determine its center and fix a pin P_{o} as shown. Looking from one side at the opposite end of the slab, fix pin P_{1} and then pin P_{2} so that they are in line with the image I of the pin P_{o} .On the other side locate the same image using pins P_{3} and P_{4} as shown above.
 Remove the glass block and the pins and produce lines P_{1}, P_{2} and P_{3}, P_{4} to their points of intersection; (the position of the image I) (1mark)
 Determine the midpoint of AD and label it Q. Measure the lengths QP_{o} and Q_{1}. (2marks)
QP_{o} =..............................cm
Q_{1} =.................................cm  Work out the ratio =(QP_{o}) =n (1 mark)
Q_{1}  What does n represent (1mark)
QUESTION 2
You are provided with the following
 Two dry cells
 A voltmeter
 A cell holder
 An ammeter
 Five connecting wires
 A nichrome wire mounted on a meter rule and labeled Q
 A jockey
PROCEED AS FOLLOWS
 Set up the apparatus as shown
 By disconnecting the jockey from the nichrome wire ,read and record the ammeter reading I and the corresponding voltmeter reading E. (2marks)
I = ...............................A
E = ..................................V  With the jockey placed at the following lengths, read and record the ammeter reading and the corresponding voltmeter reading. Compete the table below. 6mks
Length L (cm) 70 50 40 30 20 10 P.d V(v) Current I (A)  Plot a graph of potential difference V (yaxis) against current I , on the grid provided. (5marks)
 Determine the slope S of the graph. (2marks)
 Given that the equation connecting V, E, I, and r is E = V + Ir, from the graph determine:
 the e.m.f of one cell. (2marks)
 the internal resistance of one cell (2marks)
 the voltage p. d when current is 0.4 A (1mark)
MARKING SCHEME


Mass m (g)
100
150
200
250
300
350
Time for 20 oscillation t (s)
6.59
8.03
9.60
10.91
11.57
12.56
Period time T (s)
0.3295
0.4015
0.4800
0.5455
0.5785
0.6280
T^{2} (S^{2})
0.1086
0.1612
0.2304
0.2976
0.3347
0.3944
* For t each correct value ½mk max 3mks
* For T all values correct 2mks more than 3 correct
1mk less than three correct 0mk. max 2mks
* For T² all values correct 1mk max 1mk 
 Gradient = âY = âT² = (0.25  0) â¹ =1.111 s²/kg â¹
âX âm (0.225  0)  y = mx +c
T² = π² M+0 = Slope = π²
K K
K = π² â¹ = π² = 8.972 N/m â¹
slope 1.11
k. Lines P_{1}, P_{2} & P_{3}, P_{4} intersecting at I â¹
l. QP_{0} = 10.0cm â¹
Q_{1}= 6.6 cm â¹
m. n=QP_{o} = 10.0 =1.5152â¹
Q_{1} 6.6
n. Refractive indexâ¹

QUESTION 2
 I= 0Aâ¹
E=3.0 ± 0.2 Vâ¹ 
@½mkLength L (cm)
70
50
40
30
20
10
p.d V (V)
2.4
2.3
2.2
2.1
2.0
1.8
±0.2v
Current 1 (A)
0.18
0.21
0.25
0.29
0.32
0.38
±0.01v
max 6mks 
 Slope = âV= (3.0 − 2.5)V â¹
âI (0 − 0.15)A
= ^{0.5}/_{0.15}= 3.33Ω â¹  y = m x +c
= −rI +E E. m. f of the battery = y intercept
= 3.0 vâ¹
since the two cell are in series, the e. m .f of one cell = ^{E}/_{2} = 1.5Vâ¹  Slope = r
therefore the internal resistance of the battery = slope
= −(3.33)â¹
=3.33â¦  Since the cells are in series, the internal resistance of one cell =^{r}/_{2} =^{3.33}/_{2} =1.665â¦â¹
 From the graph:
when 1= 0.4A
V=1.75Vâ¹
 E. m. f of the battery = y intercept