Question

A linear aperture whose width is $0.02\, cm$ is placed immediately in front of a lens of focal length $60\, cm$. The aperture is illuminated normally by a parallel beam of wavelength $5 \times 10^{-5} cm$. The distance of the first dark band of the diffraction pattern from the centre of the screen is

• A. 0.10 cm
• B. 0.25 cm
• C. 0.20 cm
• D. 0.15 cm

Answer 1

Answer: (D)

0.15 cm

Answer 2

The correct option is(D): 0.15 cm.
$x = \frac{5\times10^{-5} \times60}{ 0.02}$
$x = \frac{300 \times10^{-5}}{0.02} = 0.15 cm$