Question

What will be the angle of diffraction for the first secondary maximum due to diffraction at a single slit of width $0.4\, mm$, using light of wavelength $4000\,\mathring{A}$ ?

• A. $ 1.0\times 10^{-4}$ rad
• B. $ 0.5\times 10^{-4}$ rad
• C. $ 0.15\times 10^{-3}$ rad
• D. $ 1.5\times 10^{-3}$ rad

Answer 1

Answer: (D)

Angle of diffraction for the secondary maxima
$\theta=\frac{3}{2} \times \frac{\lambda}{a}$
$=\frac{3}{2} \times \frac{4000 \times 10^{-10}}{0.4 \times 10^{-3}}$
$=\frac{30}{2} \times 10^{-4}=15 \times 10^{-4}$
$=1.5 \times 10^{-3} rad$