A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observe on screen 1 m away. It is observed that the first minimum is at a distance of `2.5 mm` from the centre of the screen. Find the width of the slit.

Explanation

`theta = (y)/(D) , theta = ( 2 . 5 xx 10^(-3))/(1) ` radian
Now , a sin `theta = n lambda`
Since `theta ` is very small, therefore sin `theta = theta`
or `a = (n lambda)/(theta) = (1 xx 500 xx 10^(-9))/(2 . 5 xx 10^(-3))` m
`= 2 xx 10^(-4) m = 0 . 2 ` m m