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CAIE IGCSE Physics Refraction of Light Question Bank

Practise refraction ray diagrams and calculations using normals, refractive index, light speed, critical angle and total internal reflection in optical fibres.

Syllabus
2026–2028
Course
Physics 0625

Exam points

  • measure incidence and refraction angles from the normal and use the correct sine ratio
  • calculate refractive index or light speed using n = sin i/sin r or n = c/v
  • apply the critical-angle conditions and trace repeated total internal reflection in a fibre

Covered syllabus points

3.2.2.1—Terms normal, angle of incidence and3.2.2.2—An experiment to show refraction of3.2.2.3—Passage of light through a transparent3.2.2.4—Meaning of critical angle3.2.2.5—Internal reflection and total internal3.2.2.6—Refractive index, n, as the ratio of3.2.2.7—Refractive index: n = sin i / sin r3.2.2.8—Critical angle relation: n = 1 / sin c3.2.2.9—Use of optical fibres, particularly in

3.2.2 Refraction of light question 1

[Maximum number: 5]

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 Refraction of light question 1 — CAIE IGCSE Physics

soap film
```
air
```


The refractive index of the soap film is 1.28 .

Question (a)

(a)

Define refractive index in terms of the speed of light.

[ 1 ]

Question (b)

(b)

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

[ 2 ]

Question (c)

(c)

On Fig. 5.1, carefully draw the refracted light ray in the soap film and label the angle of refraction.

[ 2 ]

3.2.2 Refraction of light question 2

[Maximum number: 7]

Fig. 5.1 shows four rays of red light, P, Q, R and S, coming from a spotlight in a swimming pool.

Fig. 5.1

Fig. 5.1

Question (a)

(a)

Define, in words, refractive index for a ray of light travelling from air to water.

[ 1 ]

Question (b)

(b)

On Fig. 5.1, draw the path of rays P and Q at the water-air boundary.

[ 2 ]

Question (c)

(c)

The angle of incidence for ray R is 49∘49^{\circ}.

Calculate the refractive index of the water.
refractive index =

[ 2 ]

Question (d)

(d)

Explain why ray S is totally internally reflected at the water surface.

[ 2 ]

3.2.2 Refraction of light question 3

[Maximum number: 6]

Fig. 6.1 shows part of an optical fibre used in high-speed broadband communication.

Fig. 6.1

Fig. 6.1

Question (a)

(a)

The optical fibre is made of glass with a refractive index of 1.4.

Calculate the critical angle c.

c=
[ 3 ]

Question (b)

(b)

State the meaning of critical angle.

[ 1 ]

Question (c)

(c)

On Fig. 6.1, label the angle of incidence of the ray of light as it hits the wall of the glass fibre. Draw the continuation of the ray until it leaves the glass fibre.

[ 2 ]
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