Refraction of Waves

This lesson explains refraction — what happens when a wave passes from one medium to another — including ray diagrams, changes in speed and direction, and a qualitative understanding of Snell's law, as required by the Edexcel GCSE Combined Science specification (1SC0).

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What Is Refraction?

Refraction is the change in direction of a wave as it passes from one medium to another, caused by a change in speed.

Key facts:

• When a wave enters a denser medium (e.g. air → glass), it slows down.
• When a wave enters a less dense medium (e.g. glass → air), it speeds up.
• The frequency of the wave does not change during refraction — only the speed and wavelength change.

Exam Tip: Remember — when a wave changes medium the frequency stays the same. The speed changes and the wavelength changes, but not the frequency.

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Why Does the Direction Change?

Refraction occurs because one side of the wavefront reaches the new medium before the other side. The part that enters first changes speed, while the other part continues at the original speed. This causes the wavefront to change direction.