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Alliance High School
Time 21/2 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.
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)
vmin = ..... cm (1 mark)
- Determine the values of h1 and h2 from the equations below.
- (2 marks)
- Determine h, the average of h1 and h2
h = ........ (cm) (1 mark)
- From the graph determine v when u+v = 43.0 cm (2 marks)