You will investigate the refraction of light through a transparent block. You are provided with: • a rectangular transparent block • an illuminated slit • a protractor • a 30 cm ruler.

1. (a)(i)On Fig. 2.1, draw a normal to the line XY at point M. Extend the normal 8 cm above and 8 cm below the line XY.[1]
2. (a)(ii)On Fig. 2.1, draw a line from point M to the left of the normal above line XY so that the angle between the drawn line and the normal is 40°. Label the top left-hand end of the line as point L.[1]
3. (b)(i)Place the block with one of its long sides on the line XY. The top left-hand side of the block should be at point X. Draw the outline of the block on Fig. 2.1. Do not remove the transparent block.[1]
4. (b)(ii)Using the illuminated slit, shine a narrow ray of light along the line LM. Mark with small crosses (x) two points on the ray that emerges from the block. Choose the position of the points so that the ray leaving the block can be drawn accurately.[1]
5. (b)(iii)Remove the glass block. Join the marked crosses and extend the line to meet the lower end of the outline of the block. Label the point where the line meets the block outline as point P.[1]
6. (b)(iv)Draw a straight line to join the points M and P.[1]
7. (b)(v)The angle of refraction r is the angle between the line MP and the normal drawn in (a)(i). Measure and record angle r. r = ..................................................... °[1]
8. (c)The refractive index n of the transparent block is given by the equation shown. n = sin 40° / sin r Calculate n and give your answer to 2 significant figures. n = .....................................................[2]
9. (d)Suggest how you could change the experiment to make sure that your value of n is accurate.[1]

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