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3.2.2Waves

Refraction OF Light — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 10 parts Lesson 11 of 35 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

3.2.2 Refraction of Light — IGCSE PHYSICS notes: Describe refraction of light, draw ray diagrams for refraction and explain it using changes in speed.Normal — a line at right angles to the boundaryAngle of incidence i — the angle of the ray approaching the boundary, measured from…

  • Angle of refraction r
  • Less dense to more dense
  • More dense to less dense
  • Along the normal
  • Two boundaries
  • Memory aid

Part 1 of 8Ray diagrams for refraction

Normal
  • Normal a line at right angles to the boundary
Angle of incidence i
  • Angle of incidence i the angle of the ray approaching the boundary, measured from the normal
Angle of refraction r
  • Angle of refraction r the angle of the ray leaving the boundary, measured from the normal
Arrows
  • Arrows the incident ray points towards the boundary and the refracted ray points away from it

Part 2 of 8Refraction of light

Refraction
  • Refraction occurs when light passes a boundary between two different transparent materials, changing direction
Less dense to more dense
  • Less dense to more dense for example air to glass, light bends towards the normal
More dense to less dense
  • More dense to less dense for example glass to air, light bends away from the normal
Along the normal
  • Along the normal light does not bend at all

Part 3 of 8Rectangular block

Two boundaries
  • Two boundaries light meets one boundary entering and another leaving
Link
  • Link the refracted ray at the first boundary is the incident ray at the second
Memory aid
  • Memory aid enters towards the normal, leaves away from the normal

Part 4 of 8Cause of refraction

Speed
  • Speed the change in direction is due to the change in speed in different substances
More optically dense
  • More optically dense the waves slow down and bend towards the normal
Less optically dense
  • Less optically dense the waves speed up and bend away from the normal
Properties that change
  • Properties that change speed and wavelength
Frequency
  • Frequency does not change
Colour
  • Colour frequency decides the colour, and light does not change colour when it refracts

Part 5 of 8Investigating refraction

Aim
  • Aim investigate refraction using rectangular blocks, semicircular blocks and triangular prisms
Independent variable
  • Independent variable shape of the block
Dependent variable
  • Dependent variable angle of refraction
Control variables
  • Control variables width of the beam and wavelength of the light

Part 6 of 8Method with blocks

1
Place the block on paper and draw round it.
2
Direct a ray from a ray box at a side face.
3
Mark a point near the ray box, the entry point, the exit point and a point about 5 cm along the emerging ray.
4
Draw a dashed normal at right angles to the outline where the ray enters.
5
Remove the block and join the points with straight lines.
6
Repeat at a different angle and then for each block shape.
  • Analysis
    • label each path clearly and use the laws of refraction to analyse the angles

Part 7 of 8Errors and safety

Right angles
  • Right angles use a set square so the normals are exact
Marking
  • Marking use a sharp pencil and mark the middle of the beam
Protractor
  • Protractor a higher-resolution protractor gives more accurate angles
Ray box
  • Ray box can burn, so run burns under cold water for at least 5 minutes
Eyes
  • Eyes avoid looking directly into the light

Part 8 of 8More from the specification

1Virtual images and optical fibres transmission
  • Virtual images and optical fibres transmission refractive lenses produce erect virtual images,
    • while total internal reflection guides light pulses along optical fibres.
2Refraction
  • Refraction change of direction of light as its speed changes on crossing a boundary between media
3Refractive index
  • Refractive index ratio of the speed of light in air to the speed in the material, n = sin i / sin r
4Total internal reflection
  • Total internal reflection occurs when light in a denser medium meets the boundary above the critical angle, so all of it is reflected
5Lenses
  • Lenses a converging lens brings rays together to form a real or virtual image,
  • while a diverging lens spreads rays and forms a virtual image;
    • a plane mirror gives a virtual image by reflection
6Refraction
  • Refraction change of direction of light as its speed changes on crossing a boundary between media
7Refractive index
  • Refractive index ratio of the speed of light in air to the speed in the material, n = sin i / sin r
    What the symbols mean: n = refractive index (no unit) · i or θ1 = angle of incidence · r or θ2 = angle of refraction
    • (both measured from the normal)
8Total internal reflection
  • Total internal reflection occurs when light in a denser medium meets the boundary above the critical angle, so all of it is reflected
9Lenses
  • Lenses a converging lens brings rays together to form a real or virtual image,
  • while a diverging lens spreads rays and forms a virtual image;
    • a plane mirror gives a virtual image by reflection
10Distance
  • Total length of path travelled, a scalar.
11Refractive index
  • Ratio of the speed of light in a vacuum to its speed in a material
12Critical angle
  • Incline angle at which sliding just begins.
13Virtual image
  • Image formed where rays only appear to meet, not projectable on a screen
14Optical fibre
  • Thin transparent strand that guides light by TIR
15Principal focus
  • Point where parallel rays meet or appear to come from
16Focal length
  • Distance from the lens centre to the principal focus
17Plane mirror
  • Flat mirror.
18Reflection
  • Light bouncing off a surface.

Key terms

TermMeaning
RefractionChange of direction of light caused by a change of speed at a boundary
Angle of refractionAngle between the refracted ray and the normal
Optical densityHow strongly a medium slows light
NormalLine at right angles to a boundary
FrequencyNumber of waves per second, which stays the same in refraction

Avoid these mistakes

1
Saying light bends towards the normal on leaving glass — it bends away.
2
Measuring angles from the surface — measure from the normal.
3
Saying frequency changes in refraction — only speed and wavelength change.
4
Saying light changes colour in refraction — frequency and so colour are unchanged.

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