Question

Light of 6000 Å is incident on a circular hole and is received on a screen 50 cm away. What is the radius of the hole, if the intensity of light on the screen is 4 times the intensity without the hole?

(a) 0.025 cm

(b) 0.047 cm

(c) 0.054 cm

(d) 0.089 cm

I have been asked this question in an online quiz.

I need to ask this question from Fresnel and Fraunhofer Diffraction topic in chapter Diffraction of Engineering Physics II

Answer 1

Right answer is (c) 0.054 cm

To elaborate: The intensity will be 4 times than in its absence if the radius of the hole is equal to that of the first half period zone.

Therefore, radius, r  = \(\sqrt{b\lambda}\)

Here, b = 50 cm and λ = 6000 Å = 6 X 10^-5 cm

r = 0.0548cm.