Question

How does the fringe width, in Young's double-slit experiment change when the distance of separation between the slits and screen is doubled?

Answer 1

Fringe width, $\beta =\frac{\lambda D}{d}$ where all the symbols have their usual meanings.

Now the distance between the slit and screen is doubled i.e $D^{\prime }=2D$

$\therefore$ New fringe width ${\beta }^{\prime }=\frac{\lambda \left(2D\right)}{d}=2\beta$

Thus fringe width gets also doubled.