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Waves - including water waves, sound and light - can be reflected at the boundary between two different materials.

When drawing wave diagrams, it is easier to draw wave fronts rather than crests and troughs.

Each wavefronts is drawn at right angles to the wave direction.

For wave diagrams, the wave direction and wave fronts are normally drawn.

Waves, such as water waves, obey the law of reflection that states:

angle of incidence i = angle of reflection r

The angles of incidence, i, and angle of reflection, r, are measured between the wave direction and the normal – a construction line drawn at 90° to the barrier.

The diagram below shows a water wave reflected at a plane barrier.

The diagram shows that when water waves are reflected their direction changes, but their wavelength and frequency remain unchanged

Key points

When waves are reflected

• angle of incidence i = angle of reflection r;
• wavelength remains unchanged;
• frequency remains unchanged.