In this experiment, you will investigate the refraction of a ray of light passing through a transparent block and determine the refractive index n of the block. You are provided with: • a transparent, rectangular block • a 30 cm ruler • a protractor • an illuminated slit or a raybox with a slit.

1. (a)Fig. 1.2 is on page 3 of your question paper. On Fig. 1.2, draw a normal to the line PQ at the point R. Extend your normal 6cm above and at least 8 cm below PQ. Measure the angle θ between SR and the normal. θ = ...................................° [1][1]
2. (b)Place the block on Fig. 1.2, with one of its long sides along the line PQ. The top left-hand corner of the block must be at A, as shown in Fig. 1.1. [Figure 1.1] On Fig. 1.2, draw around the outline of the block. Remove the block and label the outline of the block ABCD as shown in Fig. 1.1. Mark the point where the normal crosses side BC of the block with the letter T. Replace the block and switch on the lamp. Position the illuminated slit so that a ray of light passes along the line SR towards R. On Fig. 1.2, mark with small crosses (X) two points on the ray that leaves side BC of the block. Choose the position of the points so that the ray leaving the block can be accurately marked. Switch off the lamp. [1][1]
3. (c)(i)Measure and record the length a of ET. a = ................................... cm [1][1]
4. (c)(ii)Measure and record the length b of ER. b = ................................... cm [1][1]
5. (c)(iii)Extend the line FE into the block until it meets the line RT. Label the point where FE meets RT with the letter G. Measure the length c of EG. c = ................................... cm [1][1]
6. (d)(i)Use your values for a and b from (c)(i) and (c)(ii) to calculate a first value n₁ for the refractive index of the block. Use the equation shown. n₁ = b / 2a n₁ = ................................... [1][1]
7. (d)(ii)Use your values for b and c from (c)(ii) and (c)(iii) to calculate a second value n₂ for the refractive index of the block. Use the equation shown: n₂ = b / c n₂ = ................................... [1][1]
8. (e)Two quantities can be considered to be the same within the limits of experimental accuracy if their values are within 10% of each other. Compare your value n₁ for the refractive index calculated in (d)(i) with the value n₂ calculated in (d)(ii). State if your two values can be considered to be the same. Support your statement with a calculation. calculation statement [2][2]
9. (f)One source of inaccuracy in this experiment is careless measurement. Suggest another source of inaccuracy in this experiment. [1][1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.