Electromagnetic Waves and Wave Optics: Interference with Initial Phase Difference MCQ

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Interference with Initial Phase DifferenceHardQuestion 20246

Question

Two coherent sources with a constant phase difference of π (antiphase) are placed at the slit positions in YDSE. The central fringe is:

A
Bright (constructive at centre)
B
Dark (destructive at centre)
Correct
C
Unchanged
D
Absent

Correct answer

Dark (destructive at centre)

Explanation

At the centre, geometric path difference = 0. But since sources are antiphase (phase difference π), the actual phase difference at centre = 0 + π = π → destructive interference → dark central fringe. The entire pattern shifts by half a fringe width.

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