If yellow light emitted by sodium lamp in Young's double slit experiment is replaced by monochromatic blue light of the same intensity (a) fringe width will decrease (b) fringe width will increase (c) fringe width will remain unchanged (d) fringes will become less intense

Answer: (a). β = (λ D)/(d) ∝ λ Blue light has a shorter wavelength than yellow sodium light, so β decreases; same intensity means fringes are not fainter. So the answer is (a).

If yellow light emitted by sodium lamp in Young's double slit… | NEET 1992 (AIPMT)

Q75NEET 1992 · AIPMTEasy

YDSE: Fringe Width & Fringe Positions

If yellow light emitted by sodium lamp in Young's double slit experiment is replaced by monochromatic blue light of the same intensity

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Answer: (a)

$\beta = \frac{\lambda D}{d} \propto \lambda$
Blue light has a shorter wavelength than yellow sodium light, so $\beta$ decreases; same intensity means fringes are not fainter.
So the answer is (a).

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YDSE: Fringe Width & Fringe Positions question from NEET 1992 (AIPMT)

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