Question

A narrow slit S transmitting light of wavelength λ is placed a distance d above a large plane mirror as shown in figure (17-E1). The light coming directly from the slit

and that coming after the reflection interfere at a screen ∑ placed at a distance D from the slit. (a) What will be the intensity at a point just above the mirror, i.e., just above O ? (b) At what distance from O does the first maximum occur ?

Answer 1

a) Since, there is a phase difference of π  between direct light and reflecting light, the intensity just above the mirror will be zero.
b) Here, 2d = equivalent slit separation
D = Distance between slit and screen.