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Question
State Huygens’s principle. Show, with the help of a suitable diagram, how this principle is used to obtain the diffraction pattern by a single slit.
Draw a plot of intensity distribution and explain clearly why the secondary maxima becomes weaker with increasing order (n) of the secondary maxima.
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Solution
Huygen’s principle states that
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Each point on a wave front behaves as a source of secondary wavelets
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The secondary wavelets travel with the speed of light in that medium
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The position of new wave front at a later time can be found out by drawing a common tangent to all these secondary wavelets
Intensity distribution of single slit distribution
For the first secondary maxima (n = 1), only one-third of the slit contributes to its intensity.
Secondly, for n = 2, only one-fifth of the slit contributes to the intensity.
Therefore, with increasing n, the intensity decreases.
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