Light of wavelength λ from a point source falls on a small circular obstacle

Light of wavelength λ from a point source falls on a small circular obstacle of diameter d. Dark and bright circular rings around a central bright spot are formed on a screen beyond the obstacle. The distance between the screen and obstacle is D. Then, the condition for the formaton of rings, is

Options

(a) √λ≈d/4D
(b) λ≈d²/4D
(c) d≈λ²/D
(d) λ≈D/4

Correct Answer:

λ≈d²/4D

Explanation:

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