alleryIn a double-slit experiment, if the wavelength is doubled and the slit separation is halved, the fringe width becomes
A1/4 of original
B4 times original
C2 times original
DSame as original
Answer & Solution
Correct answer: B. 4 times original
1. β = λD/d. New wavelength = 2λ; new slit separation = d/2.
2. New β = (2λ)D / (d/2) = 4 × (λD/d) = 4β.
3. So the fringe width becomes 4 times the original.
4. Screen distance D was kept unchanged.
_Source: syllabus Physics, Ch 10 "Wave Optics", §10.4_
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