# Wave Interference and its Types

## What is Wave Interference?

The interaction of waves travelling in the same medium causes them to get interfered with, is wave interference. Basically, when two or more waves having the same phase and frequency meet at a point while travelling in a medium, then the amplitude of waves either increase, decrease or remain the same at that point. This is called interference of waves.

Waves propagating in the same medium interfere when they superimpose on each other. Thus, wave interference is based on the principle of superposition.

### Principle of Superposition

The principle of superposition is associated with the behaviour of wave overlapping and is sometimes referred to as superposition property. It states that two or more waves of the same type when overlap while propagating in the same medium, their resultant will be such a disturbance which is the summation of each individual disturbance.

This principle is applicable to any linear system and has various applications in the field of physics and engineering.

Suppose we have 2 separate sources, P and Q. These sources generate wave a1 and wave a2, respectively.  Then according to the principle of superposition, the overall response while propagating in the same medium in the same direction will be a1 + a2.
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## Types of Interference of Wave

Wave interference is mainly classified into two categories, namely constructive interference and destructive interference.

### Constructive Interference

When two waves of the same phase and frequency travel in a medium in the same direction, then their interference at different points produces a resultant wave whose overall amplitude is the vector sum of the individual amplitude of each wave. This is what we call constructive interference.

The figure given below represents two waves propagating in the same medium and the resultant of the two waves, which is an outcome of the summation of the two waves: From the above figure, it is clear that the crest of the first waveform coincides with the crest of the second waveform. Thus giving rise to a constructive type of interference. Here both waves are of the same amplitude. Hence, the amplitude of a resultant wave is double the amplitude of a wave.

### Destructive Interference

When two waves that are not in the same phase (i.e., in out of phase relationship ) propagate in a medium in the same direction. Then their interference in the medium generates a resultant wave, whose overall amplitude is the difference between the individual amplitude of each wave. This is what we call destructive interference.

The figure given below provides you with the illustration of two waves propagating in the same medium and their resultant, which is an outcome of the difference between the two waves: From the above figure, it is clear that the crest of the first waveform is not coinciding with the crest of the second waveform. Thus giving rise to a destructive type of interference. As we have considered both the waves of the same amplitude, therefore, the two completely cancel out each other. Also, there will be complete annulment because of their equal amplitude.

You must note a point over here that when the direction of propagation of waves is opposite. Then this gives rise to a standing wave.