Question

A parallel beam of monochromatic light of wavelength $450\, nm$ passes through a long slit of width $0.2 \,mm$. What is angular divergence in which most of the light is diffracted?

• A. $4.5 \times 10^{-3} \,rad$
• B. $2 \times 10^{-4}\, rad$
• C. $4 \times 10^{-3}\, rad$
• D. $4.5 \times 10^{-4} \,rad$

Answer 1

Answer: (A)

Most of light is diffracted between two first order minima
a $\sin \theta=\lambda$
$\sin 0=0=\frac{450 \times 10^{-9}}{0.2 \times 10^{-3}}$
$=\pm 2.25 \times 10^{-3}$
Angular divergence $=2 \theta=2 \times 2.25 \times 10^{-3}$
$=4.5 \times 10^{-3} \,rad$