MCQ
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 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${\tan ^{ - 1}}\left( {\frac{{n\lambda }}{d}} \right)$
- ✓${\sin ^{ - 1}}\left( {\frac{{n\lambda }}{{2d}}} \right)$
- D${\cos ^{ - 1}}\left( {\frac{{n\lambda }}{{2d}}} \right)$
