Introduction to Interference

Interference of light is the non uniform distribution of light energy (wave) due to the superposition of coherent sources of light. Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium. When two or more waves meet together, they interfere each other and produce a resultant wave whose properties can be calculated by using principle of superposition. Superposition principle is applicable for mechanical wave as well as electromagnetic waves.

Interference through slits

Condition for interference

  • The source must be coherent.
  • The source must be close to each other.
  • The two sources should be monochromatic.
  • The light wave should be passed through very narrow slit.

Coherent sources

Two sources of light that emit the light waves of same wavelength or frequency and has always constant phase difference are called coherent sources of light. Laser light is an example of coherent source of light.

Light rays in laser

Coherent sources can be obtained from a single source when it is made to pass through multiple slits. However two independent sources of light cannot be coherent because they have different frequency and wavelength so they will have different phase difference due to the random emission of light. No interference pattern can be obtained from non coherent sources.


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