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.

Answer 1

Huygen’s principle states that

• Each point on a wave front behaves as a source of secondary wavelets

• The secondary wavelets travel with the speed of light in that medium

• 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.