3.2Unit 6: Light and objects in space

Refraction — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 11 parts Lesson 3 of 8 1 quiz

📚 Cambridge Checkpoint Physics 0893 Hub / Topical Revision

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Lesson summary

3.2 Refraction — CHECKPOINT PHYSICS 0893 notes: Explain refraction as a change of direction caused by a change in speed and draw ray diagrams for light entering and leaving glass or water.Medium = the material that light passes through, such as air, glass or waterDistorted views …

Slowing down
Roller skate analogy
Ray of light
Measured from
Windscreen wipers
Uses of lenses

Part 1 of 9What refraction is

Medium

Medium the material that light passes through, such as air, glass or water

Distorted views

Distorted views looking through a glass of water or a wet window is unclear because of refraction

Refraction

Refraction the change in direction of light on passing from one medium to another because of a change in speed

Part 2 of 9Speed of light in different media

Medium	Speed of light (km/s)
Air	300 000
Water	225 000
Glass	200 000

Part 3 of 9Why light changes direction

Slowing down

Slowing down light travels more slowly in water and glass than in air

Roller skate analogy

Roller skate analogy a skater whose one skate enters grass slows on that side and turns

Ray of light

Ray of light one side of the ray slows first, so the ray changes direction

Part 4 of 9Air into glass or water

Speed

Speed the light slows down

Bending

Bending the ray bends towards the normal

Angles

Angles the angle of incidence is greater than the angle of refraction

Measured from

Measured from both angles are measured from the normal

Part 5 of 9Glass or water into air

Speed

Speed the light speeds up

Bending

Bending the ray bends away from the normal

Angles

Angles the angle of refraction is greater than the angle of incidence

Part 6 of 9Refraction compared with the normal

Direction of travel	Speed	Bends	Angle comparison
Air to glass or water	Slows down	Towards the normal	Incidence greater than refraction
Glass or water to air	Speeds up	Away from the normal	Refraction greater than incidence
Along the normal	Changes speed	No change in direction	Both angles zero

Part 7 of 9Refraction in everyday life

Nuisance

Nuisance water drops on a window refract light in different directions, so it is difficult to see

Windscreen wipers

Windscreen wipers they remove the drops so refraction through the glass is in one direction

Lenses

Lenses curved pieces of glass designed to refract light in a known way

Uses of lenses

Uses of lenses eyes, cameras, phones and glasses

Part 8 of 9Effects of refraction

Appearing coin

Appearing coin a coin hidden behind the cup edge comes into view when water is added because rays bend at the surface

Broken pencil

Broken pencil a pencil in water appears broken at the surface

Water and oil

Water and oil refraction differs when oil lies on water, showing light speed differs in the two liquids

Part 9 of 9Drawing accurate refraction diagrams

Draw round a rectangular glass block on white paper.

Direct a ray from a ray box at the block at an angle.

Mark the incident ray in two places and the emerging ray in two places.

Remove the block and join the points with a ruler.

Draw normals at both surfaces and measure the angles.

Repeat with different angles, including an angle of incidence of zero.

Key terms

Term	Meaning
Refraction	Change in direction of light when it changes speed between media.
Medium	Material through which light travels.
Normal	Line at 90° to the surface.
Angle of refraction	Angle between refracted ray and normal.
Lens	Curved piece of glass that refracts light.
Distorted	Changed to be less clear.

Avoid these mistakes

Measuring refraction angles from the surface — they are measured from the normal.

Thinking light speeds up in glass — it slows down.

Thinking light bends towards the normal on leaving glass — it bends away from the normal.

Thinking a ray along the normal bends — it passes straight through without changing direction.

Last updated: 12 October 2026