A monochromatic beam of light fall on YDSE apparatus at some angle (say `theta`) as shown in figure. A thin sheet of glass is inserted in front of the lower slit `s_(2)`. The central bright fringe (path difference `= 0`) will be obtained

Options

A. at O
B. above O
C. below O
D. anywhere depending on angle `theta`, thickenss of plate t, and refractive index of glass `mu`

Answer

D

Explanation

If `d sin theta = (mu - 1) t`, central fringe is obtained at O.
If `d sin theta gt (mu - 1 ) t`, central fringe is obtained above O.
If `d sin theta lt (mu - 1)t`, central fringe is obtained below O.