# PHYSICS PAPER 3 - 2019 KCSE CEKENA MOCK EXAMINATION (QUESTIONS AND ANSWERS)

INSTRUCTIONS TO CANDIDATES

• Mathematical tables and electronic calculators may be used.
• All workings MUST be clearly shown necessary.
1. You are provided with;
• A Marble/bob with a piece of the thread attached.
• Two wooden blocks.
• Clamp, stand & a boss
• Metre rule.
• ½ metre rule supported on a wooden block.
• 2 pieces of cello tape.
• Stop watch.

Procedure:
1. Fix the thread between the wooden blocks and fasten in the clamp. Adjust the thread so that the length, L, shown in the figure below is 50cm.
2. Fix the metre rule horizontally to the bench using the cello tape provided.
3. Adjust the clamp so that the marble is next to the end of the metre rule as shown above.
4. Displace the marble by a horizontal distance X =20cm and measure the corresponding vertical displacement h=____________ cm.    (1mark)
5. Repeat the experiment to find h for each of the following values of X and complete the table. (5mks)
 X cm h (cm) X2cm2 X2/h cm 20 25 30 35 40 45
6. plot a graph of x2/hagainst h. (5mks)
7. Determine the slope of the graph.    (2mks)
8. From the graph find the value of x2/h when h=0     (1mk)
• With the metre rule and half-metre removed — displace the marble through a horizontal distance of about 10cm and let it to swing freely, Time 20 oscillations.
1. Time for 20 oscillations                                               (lmk)
2. Determine periodic time, T
3. Periodic time, T=                                             (1 mk)
4. Calculate the value of P from the following equations.                                            (4mks)
g= 9.8m/s2
2. You are provided with the following apparatus
• A metre rule
• plasticine
• Bi convex lens
• A candle
• A lens holder
• Across wire mounted on a cardboard
• A white screen
1. Determine the focal length of the lens using a distant object.
F=  (lmk)
2. Briefly explain the method you have used above.                                                      (3mks)
3. Set up the apparatus as shown
4. Starting with u=30cm, vary the position of the screen S until a sharp image of the cross wire is observed on the screen. Measure and record the value o the image distance v.
5. Repeat the experiment above for other values of u=35cm, 40cm, 50cm, and 55cm.     (4marks)
 U (cm) 30 35 40 45 50 55 V(cm) M =v/u
6. Plot a graph of M against v. (5marks)
7. Determine the slope of the graph. (3marks)
8. The equation of the graph is given by M = v/f-1,use the graph to obtain the value of (3marks)

## MARKING SCHEME

1.
1. h = 4.0 ± 0.5                                                                            ✓(1mk)
2.
 h(cm) x/h(cm) 4.0 100.00 6.0 104.18 9.5 94.74 14.0 87.50 20.0 80.00 29.0 69.83

3.
4. Shown on graph
-by student graph.
2.
1. F = 20 ± 0.1 cm.
2. focus a distant object image is formed at f, measure the distance which is f
3.
 U 30 35 40 45 50 55 V 58 47 42 46 34.5 32.5 M =v/u 1.93 1.34 1.05 1.02 0.69 0.59
4.
5. Slope = 1/f
6. Use the x intercept
When M=0, v = f.
Or
reciprocal of slope =f.

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