In a Young's double-slit experiment, the slit separation is increased from 0.2 mm to 0.4 mm. The percentage change in fringe width is:
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Question

In a Young's double-slit experiment, the slit separation is increased from 0.2 mm to 0.4 mm. The percentage change in fringe width is:

G1 Physics · Accepted Answer

Fringe width is β = λD/d. Thus, β ∝ 1/d. When slit separation doubles from 0.2 mm to 0.4 mm, β_new = β_old/2. Decrease in fringe width: Δβ = β_old - β_new = β_old/2. Percentage decrease: (Δβ/β_old)×100 = (1/2)×100 = 50%. Therefore the fringe width decreases by 50%. Correct option: B.