Optics

# Difference between interference and diffraction of light The basic difference between interference and diffraction is that interference is the superposition of a few secondary wavelets while Diffraction is the superposition of a very large number of secondary waves.

## Interference of light

The modification in the distribution of light energy due to the superposition of two or more waves is called interference of light.

### Conditions for interference

• Light source should be monochromatic.
• The light source should be coherent mean they should not be independent but should be a subsidiary source and derived from a single source.
• The light source should be narrow and have the same intensity.
• For constructive interference path difference between light, rays should be an odd integral multiple of the wavelength of light.

path difference =0,λ ,2λ, 3λ,———–mλ

Where m=0,1,2,3,………

• For destructive interference, the path difference between the light rays should be an odd integral multiple of half the wavelength of light.

Path difference = λ/2 ,3λ/2 ,5λ/2 ,7λ/2 ,…………… (m+ 1 λ/2)

Where m= 0,1,2,3,…..

## Diffraction of light

The bending of light around an obstacle is called diffraction of light. The bending of light the diffraction effect depends upon the size of the obstacle. Diffraction effects are large if the edges of the obstacle are sharp and aperture is comparable in size of the wavelength of light of the order of 10 ¯7 m.

Diffraction of light is of two types:

• Fresnel Diffraction
• Fraunhofer diffraction

### Difference table of interference and diffraction

 Interference Diffraction 1: Interference is due to the interaction of light coming from two different wavefronts originating from the same source. 1:Diffraction is due to interaction of light coming from different parts of the same wavefront. 2:Interference fringes are of the same width. 2:Diffraction fringes are not of the same width. 3:  All bright fringes are of the same intensity. 3:All bright fringes are not of the same intensity. 4:All point of minimum intensity are perfectly dark. 4:All point of minimum intensity is not perfectly dark. 5:The spacing between fringes is uniform. 5:The spacing between fringes is not uniform.

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