Physics 0625 · IGCSE · Light

Light — practice question

A student examines how light is reflected by a plane mirror. The student’s full-size ray-trace is shown in Fig. 1.1.
(a)[1]

The student: draws line LN; labels the midpoint of LN with the letter M; draws a line PR parallel to LN and 10.0 cm below it. On Fig. 1.1, draw a normal to LN at the point M. Carry the normal downward until it meets the line PR. Mark the point where the normal meets PR with the letter Q.

(b)[2]

On Fig. 1.1, draw a line of length 14.0 cm from point M at an angle $\theta = 10^\circ$, as illustrated in Fig. 1.2. Label the other end of the line O.

(c(i))[1]

On Fig. 1.1, draw a line connecting M to X1 and X2. Extend the line until it crosses PR and label the point where it crosses PR with the letter T.

(c(ii))[1]

Measure the length a of the line QT in centimetres to the nearest millimetre and the length b of the line MT in centimetres to the nearest millimetre. Write your measurements below and in Table 1.1.

(d)[2]

Calculate the ratio $r = \frac{a}{b}$. Enter your answer in Table 1.1. Give your answer to 2 significant figures.

(e)[2]

State if you agree with the student. Use values from Table 1.1 to justify your answer.

(f)[1]

Suggest what the student can do to have more confidence in their answer to part (e).

(g)[1]

Suggest one source of inaccuracy in this experiment, even if it is carried out very carefully.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: Normal drawn correctly (by eye), extended to cross PR and Q labelled

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