Answer to Question #193723 in Optics for AKSHAT KOTNALA

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

A real image of diffraction pattern when formed on the screen with the help of converging lens placed in path of the diffracted beam and All the rays that starts from slit AB in the same phase again make each other and it produce brightness at point O on the axis of slit as they arrive there in the same phase , The intensity of beam is different , in the different directions and there are some directories as there is no light ,Thus diffraction pattern ,on screen consists of a central bright band and other dark and bright bands of decreasing intensity on both sides.

we assume a plane wave front PQ incident on the narrow slit AB. According to Huygens principle each point t on other part of wavefront PQ sends out second wavelets in different directions , Their total effect at any distant point can be find y summing the many waves arriving there from the principle of superposition , and The second waves, from points at the center C of the slit which is on portion CA and CB of wave front moves in the same distance , and in reaching at O and then the path difference between them becomes zero ,The waves intracts and combines and give rise to the central maximum at point O