Edexcel IGCSE Physics 3.18 Refractive index equation

Practise using refractive index formulae with measured angles, sine values and diagrams, including show-that and colour refraction questions.

Exam points

state or rearrange n = sin i / sin r, avoiding direct angle ratios
substitute measured angles into sine form to calculate refractive index
predict how a ray path changes when one colour has a different refractive index

[Maximum number: 3]

This question is about refraction.

(a)

The diagram shows a ray of light from a torch incident on the surface of a pool of water.

Figure for Question (a) — Edexcel IGCSE Physics

The angle of refraction of the ray of light is $33^{\circ}$

[ 3 ]

(i)

State the formula linking refractive index, angle of incidence and angle of refraction.

[ 1 ]

(ii)

Show that the refractive index of water is about 1.3

[ 2 ]

Marking points:
- substitution
- evaluation to at least 3 significant figures

Example:
$n=\frac{\sin45^\circ}{\sin33^\circ}$ n=1.30

Do not accept:
- 45/33
- 1.36

Marking guidance:
- reverse argument scores 1 mark only, e.g. calculating i or r using n
- allow $1.298\ldots$
- condone 1.29

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3.18 Refractive index equation question 1

Question (a)

Question (i)

Question (ii)