A beam with wavelength `lambda` falls on a stack of partially reflecting planes with separation `d`. The angle `theta` that the beam should make with planes so that the beams reflected from successive planes may interfere constructively is (where n=1, 2, ...)

Options

A. `sin^(-1)((nlambda)/d)`
B. `tan^(-1)((nlambda)/d)`
C. `sin^(-1)((nlambda)/(2d))`
D. `cos^(-1)((nlambda)/(2d))`

Answer

C

Explanation

Path difference `Deltax=2d sintheta=nlambda`
`sin theta=(nlambda)/(2d)`
`theta=sin^(-1)((nlambda)/(2d))`