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

\[{{\cos }^{-1}}\left( \frac{n\lambda }{2d} \right)\]

\[{{\sin }^{-1}}\left( \frac{n\lambda }{d} \right)\]

\[{{\tan }^{-1}}\left( \frac{n\lambda }{d} \right)\]

\[{{\sin }^{-1}}\left( \frac{n\lambda }{2d} \right)\]

A beam with wavelength l falls on a stack of partially reflecting plan

1.	A beam with wavelength l falls on a stack of partially reflecting planes with separation d. The angle q that the beam should make with the planes so that the beams reflected from successive planes may interfere constructively is (where n =1, 2,??)
A.	\[{{\sin }^{-1}}\left( \frac{n\lambda }{d} \right)\]
B.	\[{{\tan }^{-1}}\left( \frac{n\lambda }{d} \right)\]
C.	\[{{\sin }^{-1}}\left( \frac{n\lambda }{2d} \right)\]
D.	\[{{\cos }^{-1}}\left( \frac{n\lambda }{2d} \right)\]
Answer» D. \[{{\cos }^{-1}}\left( \frac{n\lambda }{2d} \right)\]