Question

A parallel beam of wavelength $\lambda=450 \times 10^{-9} m$ passes through a long slit of width $2 \times 10^{-4} m$. The angular divergence for which most of light is diffracted is

• A. $5.4 \times 10^{-4} rad$
• B. $4.5 \times 10^{-3} rad$
• C. $3.5 \times 10^{-3} rad$
• D. $2.8 \times 10^{-4} rad$

Answer 1

Answer: (B)

Most of the light is diffracted between the two first order minima.
$\therefore $ Required angle $=2 \theta$
$=2 \sin \theta=\frac{2 \lambda}{d}=\frac{2 \times 450 \times 10^{-9}}{2 \times 10^{-4}} $
$=450 \times 10^{-5} \text { radian }$
$=4.5 \times 10^{-3} \text { radian }$