# 8.1.1 The Principle of Superposition

### The Principle of Superposition

• The principle of superposition states that when two or more waves with the same frequency travelling in opposite directions overlap, the resultant displacement is the sum of displacements of each wave
• This principle describes how waves which meet at a point in space interact
• When two waves with the same frequency and amplitude arrive at a point, they superpose either:
• in phase, causing constructive interference. The peaks and troughs line up on both waves. The resultant wave has double the amplitude
• or, in anti-phase, causing destructive interference. The peaks on one wave line up with the troughs of the other. The resultant wave has no amplitude

Waves in superposition can undergo constructive or destructive interference

• The principle of superposition applies to all types of waves i.e. transverse and longitudinal

#### Exam Tip

The best way to draw the superposition of two waves is to find where the superimposed wave has its maximum and minimum amplitudes. It is then a case of joining them up to form the wave. Where the waves intersect determines how much constructive or destructive interference will occur.

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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