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Why do scientists think that light and sound are waves?

Total internal reflection

You should be able to describe a use of total internal reflection with the help of a diagram.

Beyond the critical angle

Waves going from a dense medium to a less dense medium speed up at the boundary. This causes light rays to bend when they pass from glass to air at an angle other than 90º. This is refraction.

Beyond a certain angle, called the critical angle, all the waves reflect back into the glass. We say that they are totally internally reflected. Have a go at the animation to check your understanding of this.

All light waves, which hit the surface beyond this critical angle, are effectively trapped. The critical angle for most glass is about 42 °.

Optical fibres

An optical fibre is a thin rod of high-quality glass. Very little light is absorbed by the glass. Light getting in at one end undergoes repeated total internal reflection, even when the fibre is bent, and emerges at the other end.

Diagram showing how light reflects inside a glass fibre - the light "zig-zags" from one side of the fibre to the other

Optical fibres

  • Optical fibres are used in endoscopes that allow surgeons to see inside their patients.
  • Optical fibres can also carry enormous amounts of information as pulses of light.

Back to Wave model of radiation index

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