A student investigates the refraction of light through a transparent block.

1. (a)(i)Fig. 2.1 shows a top view of the transparent block. On Fig. 2.1, draw a normal to the line XY at point M and extend it above and below the line XY.[1]
2. (a)(ii)Draw a line from M at an angle of 40° to the normal to the left of the normal above line XY so that the angle between the drawn line and the normal is 40°. The 40° angle is the angle of incidence. Label the top left-hand end of the line as point L.[1]
3. (b)(i)The student uses an illuminated slit to shine a narrow ray of light along the line LM. The student marks the emerging ray with two crosses as shown in Fig. 2.1. Join the marked crosses and extend the line to meet the lower end of the outline of the block. Label this as point P.[1]
4. (b)(ii)Join the points M and P with a straight line.[1]
5. (b)(iii)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]
6. (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]
7. (d)Suggest how you could change the experiment to make sure that your value of n is accurate.[1]
8. (e)Theory states that the angle between the emerging ray and the normal at the point that the ray emerges should be the same as the angle of incidence. In (a)(i), the angle of incidence is given as 40°. Add another normal to your diagram. Measure and record the angle α between the emerging ray and the normal. α = ° Explain whether your measurements agree with this theory.[2]

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