A student investigates the refraction of a ray of light passing through a transparent block and determines the refractive index n of the block. The student's ray-trace sheet is shown full size in Fig. 1.1. The outline of the transparent block is shown by the rectangle ABCD. A line SR that meets side AD of the block is also marked. [Figure 1.1]

1. (a)On Fig. 1.1, draw a normal to the block at the point R. Extend your normal 6cm above side AD and below side BC. Label the point where the normal crosses side BC of the block with the letter T. Measure the angle θ between SR and the normal. θ = .............................................. ° [1][1]
2. (b)The student: • positions an illuminated slit on the ray-trace sheet so that a ray of light passes along the line SR towards R • marks with small crosses (x) two points on the ray that leaves side BC of the block • removes the transparent block. On Fig. 1.1, draw a straight line through the two crosses to meet side BC of the block. Label the point where this line meets side BC with the letter E. Label the other end of this line as F. Draw a straight line from E to R. This shows the path of the ray of light through the block. [1][1]
3. (c)(i)Measure the length a of line ET on Fig. 1.1. a = .............................................. cm [1][1]
4. (c)(ii)Measure the length b of line ER on Fig. 1.1. b = .............................................. cm [1][1]
5. (d)On Fig. 1.1, 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 line EG on Fig. 1.1. c = .............................................. cm [1][1]
6. (e)(i)Use your values 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. (e)(ii)Use your values from (c)(ii) and (d) to calculate a second value n₂ for the refractive index of the block. Use the equation shown. n₂ = b / c n₂ = .............................................. [1][1]
8. (f)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 (e)(i) with the value n₂ calculated in (e)(ii). State if your two values can be considered to be the same. Support your statement with a calculation. calculation ............................................................................................................................................................................................................................................ statement ............................................................................................................................................................................................................................................ [2][2]
9. (g)One source of inaccuracy in this experiment is careless measurement. Suggest another source of inaccuracy in this experiment. ............................................................................................................................................................................................................................................ [1][1]

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