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Difference between interference and diffraction

Interference of light:

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

Conditions for interference:

  • Light source should be monochromatic.
  • Light source should be coherent mean they should not be independent but should be subsidiary source and derived from a single source.
  • The light source should be narrow and have same intensity.
  • For constructive interference path difference between light  rays should be odd integral multiple of 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 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 obstacle.Diffraction effects are large if the edges of the obstacle are sharp and aperture are comparable in size of the wavelength of light of the order of 10 ¯7 m.

Diffraction are of two types:

  • Fresnel Diffraction
  • Fraunhofer diffraction

Difference table of interference and diffraction:

   Interference                  Diffraction
1: Interference is due to interaction of light coming from two different wave fronts originating from the same source. 1:Diffraction is due to interaction of light coming from different parts of the same wave front.
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 are not perfectly dark.
5:The spacing between fringes is uniform.                                                                                                    5:The spacing between fringes is not uniform.

 

Related topics in our website are:

  • difference between constructive and destructive interference
  • diffraction grating
  • newton’s rings
  • refraction of light

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