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# Class 12 Interference Notes - Physics NEB Guide

## Interference of light waves Notes

### 1. Define the Superposition of waves.

→ When two or more waves meet at a point, the resultant disturbance or displacement of the medium at that point is the vector sum of the disturbances caused by those waves taken individually. This is called the general principle of the superposition of waves.

### 2. Define the Interference of light waves.

→ When a source of light is single, the distribution of energy in a medium is uniform. But when there are two sources with the same wavelength and frequency having the same phase or with a constant phase difference, then due to the superposition of two waves, the distribution of energy in the medium is not uniform. Thus, when the two waves superimpose then the resultant amplitude in that region is different from the amplitude of individual waves. The non-uniform distribution of light energy due to superposition of light waves is called interference.

There are two types of interference. They are constructive interference and destructive interference.

### 3. Define Constructive interference.

→ The interference obtained at a point where the crest of one wave falls upon the crest of the other or the trough of one falls upon the trough of the other is called constructive interference.

In such interference, the amplitude of the resultant wave is the sum of the two amplitudes. Hence, the amplitude will increase.

### 4. Define destructive interference.

→ The interference obtained at a point where the crest of one wave falls on the trough of the other wave is called destructive interference.

In such interference, the amplitude of the resultant wave is the difference between the two amplitudes. Hence, the amplitude decreases.

## Interference of light waves PDF

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