Question

A long narrow horizontal slit is placed 1 mm above a horizontal plane mirror. The interference between the light coming directly from the slit and that after reflection is seen on a screen 1.0 m away from the slit. Find the fringe-width if the light used has a wavelength of 700nm

Answer 1

Given that,

$D=1m,\lambda =700nm=700\times {10}^{-9}m$
Siince, $a=2mm,d=2a=2mm=2\times {10}^{-3}m$ ($L$ loyd's mirror experiment)

Fringes width $=\frac{\lambda D}{d}=\frac{700\times {10}^{-9}m\times 1m}{2\times {10}^{-3}m}=0.35mm$