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**Alliance High School****Physics Department****Pre-Trial Exams**

Physics

Paper 232/3

May 2018

Time 2^{1}/_{2} hours

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 allowed reading the whole paper carefully confirming that you have all the necessary apparatus before commencing your work.
- Marks are awarded for a clear record of observations actually made, their suitability, accuracy and the use made of them.
- Candidates are advised to record their observations as soon as they are made.
- Non-programmable silent electronic calculators and KNEC mathematical tables may be used except where stated otherwise.

**Question 1**

You are provided with the following apparatus.

- a candle
- a metre rule
- a white screen labelled S
- A lens labelled L, mounted on a lens holder
- Crosswires labelled O, mounted on a cardboard
- A match box
- some plasticine

Proceed as follows

- Place a metre rule on a bench and hold it in position using plasticine. Arrange the screen S, the lens L, and the crosswires O along the edge of the metre rule as shown in figure 1. The crosswires should be placed net to the zero centimeter mark. The distance between O and L are marked u and the distance between L and S marked v.
- Light the candle and place it next to the crosswires such that the flame is at the same level with the crosswires and the crosswires coincide with the middle part of the flame (white part)
- Adjust the position of the lens so that u = 15cm. Now adjust the position of the screen S until a sharp image of the crosswires is obtained on the screen S. Record the corresponding value of v in table 1.
- Repeat the procedure in (c) above for other values of u equal to 17,19,21,23,25,27 and 29 cm. Complete table 1. (8 marks)

u(cm) v(cm) u+v(cm) 15 17 19 21 23 25 27 29 - On the grid provided below, plot a graph of u + v (Y axis) against v (5 marks)
- From the graph, determine the minimum value of u+v and give the corresponding value of v.

(u + v)_{min }= ..... cm (1 mark)

v_{min}= ..... cm (1 mark) - Determine the values of h1 and h2 from the equations below.
- (2 marks)
- Determine h, the average of h
_{1}and h_{2}

h = ........ (cm) (1 mark)

- From the graph determine v when u+v = 43.0 cm (2 marks)

**Question 2**

You are provided with the following apparatus.

- A resistance wire mounted on a millimeter scale
- Two new dry cells in a cell holder
- A voltmeter
- Five connecting wires, at least one with a crocodile clip at one end

Proceed as follows.

- Set up the circuit as shown in figure 2 below and determine the combined electromotive force E of the cells.

Electromotive force E = ..... (1 mark) - Arrange the circuit as shown in figure 3. Connect the wire with the crocodile clip or jockey key on the mounted wire at a length
*l*of 10cm from the end marked A. Record the voltmeter reading in table 2 below. - Repeat the procedure in (b) above for the following values of length
*l:*20cm, 30cm, 40cm, 50cm and 60cm. Complete table 2.

L(cm) V(volts) E-V(volts) ^{V}/_{E-V}10 20 30 40 50 60 - Plot a graph of
^{V}/_{E-V}against*l*(5 marks) - Determine the slope of the graph. (3 marks)
- The equation of the graph is given by
^{V}/_{E-V }= a*l*+ b, determing the value of a and b. (2 marks) - Given that 4br = 10, where r is the internal resistance of the cells, determine the value of r. (2 marks)

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