In YDSE if a slab whose refractive index can be varied is placed in front of one of the slits. Then, the variation of resultant intensity at mid-point of screen with `mu` will be best represented by `(mu is greater than or equal to 1)

Options

A.
B.
C.
D.

Answer

C

Explanation

Shift = `((mu-1)tD)/d`
At `mu =1, shift=0`
` (##DCP_V05_C32_E01_065_S01.png" width="80%">
Therefore, intensity at centre is maximum or `I_0`.
As `mu` increases fringes shift upwards as shown in figure.
So, intensity at P first decreases to zero (as Q
reaches at P), then it further increases to `I_0`(as
point R reaches to P).