Question

A parallel beam of monochromatic light of wavelength 450 m passes through a long slit of width 0.2 mm. find the angular divergence in which most of the light is diffracted.

Answer 1

Correct Answer - `4.5 xx 10^(-3) rad`.
Most of the light is diffracted between the first order minima on either side of central maximum, for which
`sin theta = +- (lambda)/(d) = +- (450 xx 10^(-9))/(0.2 xx 10^(-3)) = +- 2.25 xx 10^(-3)`
As `sin theta` is small, thereore, `sin theta ~~ theta`
`:. theta = +- 2.25 xx 10^(-3) radian`.
Angular diverging `= 2 theta = 4.5 xx 10^(-3) rad`