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

When `mu=1` i.e., no change in path difference due to optical path difference so that mid point of the screen is again the central bright fringe.
But when `mugt1` the central bright will shift according `(D)/(d)(mu-1)t`
As `mu` increases, CBF will shift upwards from midpoint i.e., at mid point. Less bright fringe appears and when the shifts is equal to value of fringe width, the dark (zero intensity) will appear.
or Intensity variation
`O-=`central bright fringe
`y-=`distance from 'O' screen

* When `mu` increases, the fringe patterns shift towards the slit when introduced shift `(D(mu-1))/(t)` from the above two fact variation in I with `mu` is