Question

In Young's double slit experiment the two slits are $0.6\, mm$ distance apart. Interference pattern is observed on a screen at a distance $80\, cm$ from the slits. The first dark fringe is observed on the screen directly opposite to one of the slits. The wavelength of light will be _______$nm$.

Answer 1

$d=0.6 \times 10^{-3}$
$D=80 \times 10^{-2}$
$1$ st Dark fringe $=\frac{D \lambda}{2 d}=\frac{d}{2}, \lambda=\frac{d^{2}}{D}$
$=450 \times 10^{-9} m$