Explain the Young's experiment, arrangement and experiment to produce interference pattern.

Explanation

The British physicist Thomas Young made a ingenious technique to obtain coherent sources by the division of a wavefront and demonstrated a stationary interference.
An experimental arrangement of Young.s experiment is shown in the figure (a).

S = small hole on screen A. `S_(1), S_(2)` = two pinholes parallel to screen `A,S_(1)` and `S_(2)` are two pinholes on screen B and distances `SS_(1)=SS_(2)`, he distance between screen A and screen B is small in the order of mm). C = screen parallel to B and a screen is at D distance in the order of meters.
Hole S is lit by a bright source, light spread out from S and fall on both `S_(1)` and `S_(2)`. Distance `SS_(1)` and `SS_(2)` are equal so they behave like two coherent sources.
Because light waves coming out from `S_(1)` and `S_(2)` are derived from the same original source and any abrupt phase change in S will manifest in similar phase change (equal) in the light coming out from `S_(1)` and `S_(2)`
Thus, the two source `S_(1)` and `S_(2)` will be locked in phase. Thus they will become coherent sources.