Part (a) This question was fairly popular among the candidates and it was poorly attempted.

Most responding candidates could plot the graph. The determination of K was a problem to most candidates.

Part (b): Was poorly attempted by most candidates. They could neither define properly the principal focus.

Candidates are expected to:

(i) Measure and record **d**o correctly to at least 1 d.p in cm.

(ii) Correctly measure and record **five** values of **x** to at least 1 d.p in cm.

(iii) Correctly measure and record **five** values of **y** to at least 1 d.p in cm and in trend

(Trend: As **x** increases, **y **decreases)

(iv) Correctly measure and record **five** values of **d**i to at least 1 d.p. in cm and in tre

(v) Show composite table containing **x, y**, and **d**i.

Plot a graph using reasonable scales:

- draw line of best fit.

- determine the slope of the graph.

- deduce the value of **K** given that d*i* = ( ) y

- state any **two** of the following precautions.

e.g - collinearity of object, lens and screen ensured.

- Parallax error avoided on metre rule

- Zero error avoided/corrected on metre rule

- Repeated readings (shown on table)

In part (b), the expected answers are:

(i) The principal focus of a converging lens is the point on its principal axis where all rays parallel and close to it converge after refraction through the lens.

To score (i) Object must be at 2f.

(ii) Correct image must be at 2f on the other side.

(iii) Any** two** correct rays from the object intersecting to form the image.