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

Options

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

Answer

C

Explanation

For first minimum path diff. `rarr lambda//2`
phase diff. `rarr (2 pi)/(lambda) xx` path diff.
`= (2 pi)/(lambda) xx (lambda)/(2) = pi`