KNEC KCSE Physics Paper 3 – 2015 – Machakos County Trial

You are provided with the following apparatus

• A metre rule
• Two stands
• A pendulum bob
• Some plasticine
• Stop watch
• Two pieces of strings (long and short one)

Proceed as follows:
(a)Attach one end of the length of string to the metre rule at 10cm mark. Mark by use of a sliding loop of string round the meter rule.
(b)Fix the string at this point with the small bob of plasticine.
(c)Tie the string in a second loop at 90cm mark so that the string is stretched tight between the two marks.
(d)Fix this loop with a small plasticine. Attach the pendulum bob to the centre of the string so that the centre of gravity is 15cm below the point of suspension.
(e)If the attachments of the pendulum bob to the pieces does not produce a V-shape. Squeeze the string at the knot between the thumb and the fore finger.

i. Measure the angle 2θ (1mk)
ii. Pull the pendulum bob towards you through a small distance, release it; measure the time (t) of the motion by timing 10 oscillations.
iii. Remove the plasticine at B and slide the loop towards A by 4cm and repeat (ii) above for other distances AB as shown in the table below.

Table (a)

(8marks)

(a) Plot a graph of T₂ against Cosθ (5 marks)

(b) Find the slope “s” of the graph. (3 marks)
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(c) Given that find k. (2 marks)
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You are provided with the following set of apparatus

• A metre rule
• A white screen
• A candle
• Lens and lens holder

Procedure
i. Set up the apparatus as shown

ii. Starting with L1=30cm, adjust the position of the candle in order to obtain a sharp image on the screen. Record the value of L2………………………………………. (1mk)
Repeat the procedure for L1=60cm
iii. Fill and complete for values of L1/L2 below. (3 marks)
Given the equation

iii. When m=magnification determine the value of focal length f, (2 marks)
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