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

Correct answer · Option 1

\( 0.15\text{ cm} \)

Distance of first dark band \( y = \frac{\lambda D}{a} = \frac{5 \times 10^{-5} \times 60}{0.02} = 0.15\text{ cm} \).