A parallel monochromatic beam of light is incident normally on a narrow slit. A diffraction patten is formed on a screen placed perpendicular to the direction of incident beam. At the first maximum of the diffraction pattern the phase difference between the rays coming from the edges of the slit is

Options

A. `0`
B. `pi//2`
C. `pi`
D. `2pi`

Answer

D

Explanation

The path difference `(phi)` between the wavelets from the top edge and botton edge of the slit is
`phi=(2pi(a sin theta))/lambda`, a: slit width
For first minima, `sintheta=lambda//a, phi=2pi`