Interference — Condition for MinimaMediumQuestion 20250
Question
Two thin glass plates of different thickness are placed in the two slits of a YDSE. The central fringe shifts. The shift depends on:
- AAbsolute thickness of both slabs
- BDifference in optical path introduced by each slab: (n₁−1)t₁ − (n₂−1)t₂Correct
- CRefractive index of air only
- DScreen distance only
Correct answer
Difference in optical path introduced by each slab: (n₁−1)t₁ − (n₂−1)t₂
Explanation
Each slab adds (n−1)t of extra optical path to that beam. The net shift = difference in extra optical paths = (n₁−1)t₁ − (n₂−1)t₂. The fringe pattern shifts by this/β fringe widths.