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

Most of the light is diffracted between the two first order minima. These minima occur at angle given by
`a sin theta=pmnlambda`
`:. sin theta approx theta=pmlambda/a=pm(450xx10^(-9))/(0.2xx10^(-3))=+2.25xx10^(-3) " rad"`
:. The angular divergence `=2theta=4.5xx10^(-3)" rad"`