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 the incident beam. At the first minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of the slit is

Options

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

Answer

C

Explanation

A and B are the two edges of the slit of width a and the first minimum of the diffraction pattern is formed P. the path difference between the rays starting from A and B and meeting at P is `BC=asintheta_(1)`,
But `asintheta_(1)=lamda` for the first maximum,
`therefore`Phase difference`=(2pi)/(lamda)xx`path difference
`=(2pi)/(lamda)xxlamda=2pi`.