A parallel beam of light of wavelength λ is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the second minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of slit is

Options

(a) πλ
(b) 2π
(c) 3π
(d) 4π

Correct Answer:

4π

Explanation:

Condition for the diffraction minima are
Path diff. ∆x = nλ and Phase diff. ?￰ﾝﾜﾙ = 2nπ
Path diff. = nλ = 2λ
Phase diff. = 2nπ = 4π (n=2)