CBSE 2026 · Region 5 · Set 1 · Q14 · 1 mark
Assertion (A) : In Young's double-slit experiment, the fringe width for dark and bright fringes is the same.
Reason (R) : Fringe width is given by $\displaystyle \beta=\frac{\lambda \mathrm{D}}{\mathrm{d}}$, where symbols have their usual meanings.
Official answer
From CBSE’s own marking scheme for this paper.
(A)
Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Wave OpticsInterference of Light Waves and Young’s ExperimentUnderstandassertion_reasoneasy
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CBSE Class 12 Physics past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.