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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

Section 1 of 11What 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

Section 2 of 11Speed of light in different media

MediumSpeed of light (km/s)
Air300 000
Water225 000
Glass200 000

Section 3 of 11Why 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

Section 4 of 11Air 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

Section 5 of 11Glass 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

Section 6 of 11Refraction compared with the normal

Direction of travelSpeedBendsAngle comparison
Air to glass or waterSlows downTowards the normalIncidence greater than refraction
Glass or water to airSpeeds upAway from the normalRefraction greater than incidence
Along the normalChanges speedNo change in directionBoth angles zero

Section 7 of 11Refraction 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

Section 8 of 11Effects 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

Section 9 of 11Drawing accurate refraction diagrams

1
Draw round a rectangular glass block on white paper.
2
Direct a ray from a ray box at the block at an angle.
3
Mark the incident ray in two places and the emerging ray in two places.
4
Remove the block and join the points with a ruler.
5
Draw normals at both surfaces and measure the angles.
6
Repeat with different angles, including an angle of incidence of zero.

Section 10 of 11Key terms

TermMeaning
RefractionChange in direction of light when it changes speed between media.
MediumMaterial through which light travels.
NormalLine at 90° to the surface.
Angle of refractionAngle between refracted ray and normal.
LensCurved piece of glass that refracts light.
DistortedChanged to be less clear.

Section 11 of 11Exam technique

1
Measuring refraction angles from the surface — they are measured from the normal.
2
Thinking light speeds up in glass — it slows down.
3
Thinking light bends towards the normal on leaving glass — it bends away from the normal.
4
Thinking a ray along the normal bends — it passes straight through without changing direction.

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