Question

Monochromatic green light of wavelength $5 \times 10^{-7} m$ illuminates a pair of slits $1\, mm$ apart. The separation of bright lines in the interference pattern formed on a screen $2\, m$ away is (in $mm$ )?

Answer 1

$\lambda=5 \times 10^{-7} m,$
$d=10^{-3} m, $
$D =2\, m$
Separation of bright lines $=$ fringe width
$=\frac{\lambda D }{ d }$
$=\frac{5 \times 10^{-7} \times 2}{10^{-3}}=10 \times 10^{-4} m$
$=10^{-3} m =1\, mm$