CAIE IGCSE Physics 3.2.2.7 Refractive index: n = sin i / sin r

Practise using n = sin i / sin r with ray diagrams, angles to the normal, and refractive index calculations.

Exam points

substitute angles measured from the normal into n = sin i / sin r
rearrange n = sin i / sin r to calculate an unknown angle or refractive index

[Maximum number: 2]

A ray of light is incident on a soap film. Fig. 5.1 shows a magnified image of a small part of the soap film. The ray of light is refracted as it enters the soap film.

$Figure for Question 3.2.2.7—Refractive index: n = sin i / sin r question 1 — CAIE IGCSE Physics$

soap film
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air
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The refractive index of the soap film is 1.28 .

Show that the angle of refraction as the light enters the soap film is approximately $43^{\circ}$ .

$n=\frac{\sin i}{\sin r}$ OR $(r=) \sin ^{-1}\left\{\frac{\sin i}{n}\right\}$ OR $1.28=\frac{\sin 60}{\sin r}$

B1

$i=60\left({ }^{\circ}\right)$

B1

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