Question

During a straight-edge diffraction experiment, a light of wavelength 400 nm was used. What would be the position of the first minimum, if the separation between the edge and the source is 10 cm while that between the edge and eyepiece is 2 m?

(a) 1.01 cm

(b) 2.03 cm

(c) 0.57 cm

(d) 1.56 cm

This question was posed to me in an online interview.

Query is from Fresnel Diffraction topic in chapter Optics of Engineering Physics II

Answer 1

Correct option is (c) 0.57 cm

Explanation: λ = 4000 Å = 4 X 10^-5cm, a = 10 cm and b = 200 cm

Location for first maximum, x1 = \(\sqrt{\frac{2b(a+b)\lambda}{a}}\)

= \(\sqrt{0.336}\)cm

= 0.57 cm.