Q. 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
Explanation
[Solution] $y = \frac{f\lambda}{a} = \frac{60 \times 5 \times 10^{-5}}{0.02} = 0.15$ cm. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.