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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