Answer to Question #194347 in Optics for Mohd Arsalan

Question

In the Fraunhofer diffraction pattern due to a single slit, the intensity of the central 

spot is maximum. Explain on the basis of geometrical considerations.

Answer 1

1. All the rays that starts from slit AB in the same phase reinforce each other and produce brightness at point O on the axis of slit as they arrive there in the same phase
2. The intensity of diffracted beam will be different in different directions and there are some directories where there is no light
3. Thus diffraction pattern on screen consists of a central bright band and alternate dark and bright bands of decreasing intensity on both sides.
4. Figure below shows the variation of the intensity distribution with their distance from the center of the central maxima-