YDSE — Thin Film InsertionMediumQuestion 20209
Question
In YDSE, a glass slab of thickness t and refractive index n is placed over one slit. The central maximum shifts toward:
- AThe slit without the slab
- BThe slit with the slabCorrect
- CStays at the original centre
- DShifts by 2 fringe widths
Correct answer
The slit with the slab
Explanation
The slab increases the optical path length for that slit by (n−1)t. The central maximum (zero path difference) shifts toward the slab side to compensate for the extra optical path. Shift = (n−1)t × D/d fringe widths.