Explain Young's double-slit experiment,its experimental arrangement,and how it produces an interference pattern.

(N/A) The British physicist Thomas Young devised an ingenious technique to obtain coherent sources by the division of a wavefront and demonstrated a stationary interference pattern.
An experimental arrangement of Young's experiment is shown in the figure $(a)$.
$S$ is a small hole (source) on screen $A$. $S_1$ and $S_2$ are two narrow pinholes on screen $B$,parallel to screen $A$. The distances $SS_1 = SS_2$. The distance between screen $A$ and screen $B$ is small (in the order of $mm$). $C$ is a screen parallel to $B$,placed at a distance $D$ (in the order of meters).
Hole $S$ is illuminated by a bright light source. Light spreads out from $S$ and falls on both $S_1$ and $S_2$. Since the distances $SS_1$ and $SS_2$ are equal,the light waves reaching $S_1$ and $S_2$ are in phase.
Because the light waves emerging from $S_1$ and $S_2$ are derived from the same original source,any abrupt phase change in the source $S$ will manifest as an identical phase change in the light emerging from $S_1$ and $S_2$.
Thus,the two sources $S_1$ and $S_2$ are locked in phase,making them coherent sources. These coherent waves superpose on screen $C$ to produce a stable interference pattern consisting of alternating bright and dark fringes.