The candidates were required to:
(i) set up an experiment as shown in the above;
(ii) measure and record xo and five values x in cm to at least 1 decimal place and in trend. Trend: as l increases, x decreases;
(iii) evaluate five values of d and d¹;
(iv) present data on a composite and complete table showing x, l, d and d¹;
(v) correctly distinguish the graph axes, select reasonable scales, plot the five
points and draw a line of best fit;
(vi) draw a large right angled triangle on the graph line, read d¹ and ∆l, and
evaluate slope = ∆d2
(vii) show and read the intercept on the vertical axis;
(vii) deduct value of l for which d¹ = O;
(ix) state any two of the following precautions in the correct form of speech:
- parallax error in reading metre rule avoided;
- co-linearity of optical system ensured;
- repeated reading (shown on table);
- zero error of metre rule noted and corrected;
b (i) value of d¹ corresponding to l = 24; d¹ = l/d
- position of 2f shown object beyond 2f
- ray parallel to principal axis
(ii) emerging through f and ray through optical centre passing undeviated.
This question was well attempted by candidates. However, some candidates had difficulties with decimal places and correct placement of units. Some candidates also measured object and image distances instead of their sizes as demanded by the question.
The b part was fairly attempted by most candidates.