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  • what is young's double slit experiment in the air ?( ray optics)

what is young's double slit experiment in the air ?( ray optics)

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Young’s double slit experiment (YDSE)

The Young’s experiment shows that matter and energy can display both wave and particle characteristics.

Purpose of double slit experiment is as follows:-

  1. In order to prove the wave nature of light.
  2. To explain the phenomenon of interference.

Two coherent sources of light were taken in order to maintain the 0 or constant phase difference between the sources of light.

  • Experimental set-up1:-
    • Young took an ordinary source of light(S) such as light bulb.
    • The light was made to pass through a very small slit S (which was comparable with the wavelength of light).
    • The light coming from Source S was made to pass through two small slits S1 and S2 which were separated by a very small distance d.
    • One screen was kept in front of these 2 sources.

Observation1:-

  • He observed alternate dark and light bands were formed on the screen.

Setup 2:-

  • Now he took 2 light bulbs i.e. 2 non coherent sources of light and placed a screen in front of them.

Observation 2:-

  • He observed there were no alternate bands of light formed on the screen.
  • Conclusion:-
  • When coherent sources of light were taken then the phenomenon of interference is taking place.
  • When non-coherent sources were taken phenomenon of interference was not taking place.
  • The source S illuminated the sources S1 and S2 as a result the light from S1 and S2 become coherent.
  • S was the source of bothS1 and S2, therefore if there is any change in the phase of the source there will be change in the both sources also.
  • Therefore both S1 and S2 will be always in phase with each other.

 

 

Why alternate sources of light bands were seen

  • When the ordinary light source was made to pass through small slit then the wavefront of semicircle shape will be formed.
  • Wavefronts are in semicircle shape because of obstacles on both the sides.
  • In the figure red bands represents crests and yellow represents troughs.
  • When these wavefronts passes through the 2 small slits again the wavefronts will arise.
  • There will be points where red and yellow will also overlap with each other.
  • Red + Yellow and Yellow + Red à  Destructive interference à Intensity low
  • Yellow + Yellow and Red + Red à Constructive interference à Intensity high
  • Because of constructive and destructive interference there are alternate dark and light bands seen on the screen.
  • Conclusion: -
    • When the light wave is originating from the 2 coherent sources they overlap with each other both constructively and destructively.
    • As a result alternate light and dark bands of light is shown on the screen.
    • This phenomenon of overlapping of light waves giving rise to regions of higher amplitude and regions of lower amplitudeis known as interference.
    • Interference is a property related to the wave nature of the light.
    • Young’s Double slit experiment proved that the light is of wave nature which was proposed by Huygens principle.

 

  • Important resultsdrawn from the above experiment:-
  • Bands were formed as a result of interference and interference was due to the overlapping (either constructive or destructive) of waves.
  • Constructive and destructive overlapping depends on the path difference.
  • If the path difference is integral multiple of λ = constructive interference.
  • If path difference is non integral multiple of λ =destructive interference.
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