Question

In biprism experiment a source of wavelength $6500\stackrel{o}{A}$ is replaced by source of wavelength $5500\stackrel{o}{A}$. Calculate change in fringe width if the screen is at, $1$m distance from the slits which are $1$mm apart.

Answer 1

Given ${\lambda }_1=6500\stackrel{o}{A}$
${\lambda }_2=5500\stackrel{o}{A}$
$d=1mm-{10}^{-3}$m
$D=1m$
$w=\frac{DN}{d}$
$\Delta w=\frac{D}{d}({\lambda }_1-{\lambda }_2)$
$=\frac{1}{1\times {10}^{-3}}(6500-5500)\times {10}^{-10}$
$=1\times {10}^{-4}$m.