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# What is Interference and its types?

## Definition

Interference of waves occurs when two or more waves overlap at a given point.

## Type of Interference

The interference of light waves can be divided into the following two categories.

• Constructive Interference: In case of Constructive interference the crest of one wave falls on the crest of another wave in such a way that the amplitude becomes maximum. These waves are in phase with each other and have the same displacement too.
• Destructive Interference: In case of destructive interference, the crest of one wave falls on the trough of another wave in such a way that the amplitude becomes  minimum. These waves are out of phase with each other and have different displacements.

Figure : Constructive and Destructive Interference

We know that the superposition of two mechanical waves can be constructive or destructive. As i explained in case of constructive interference, the amplitude of the resultant wave at a given time or position is greater than that of either individual wave  whereas  in case of destructive interference, the resultant amplitude at a given time or position is less than that of either individual wave.

## Conditions of Interference

Sustained interference pattern simply means the position of maximum and minimum intensity regions remains constant with time. To obtain sustained interference, the following conditions are required:

• The sources must be coherent in nature.
• The two light sources must emit continuous waves of the same wavelength and have the same period.
• The distance between the two sources of light should be small to obtain fringes separated by a certain distance so that we can distinguish them.
• The sources should be monochromatic (means single wavelength).
• The two light sources must emit waves in nearly the same direction.
• The light source should be a point source.
• The distance between the two sources and the screen must be large. This condition is again important to obtain visible distinguishable fringes.

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