A thin transparent plate is inserted completely in front of the upper slit of a Young's double-slit arrangement. In which direction does the central maximum shift on the screen?
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Question

A thin transparent plate is inserted completely in front of the upper slit of a Young's double-slit arrangement. In which direction does the central maximum shift on the screen?

G1 Physics · Accepted Answer

The plate increases the optical path through the upper slit. For zero net path difference, the geometrical path from that slit to the new central maximum must be shorter. Hence the central maximum shifts toward the slit containing the plate. Correct option: B.