Two coherent sources A and B are in phase and form the endpoints of the diameter of a semicircle with AB = 6λ. An observer moves along the open semicircular arc joining A and B. How many positions of minimum intensity occur on the arc?
Physics · Wave Optics · interferece of light and huygen principle
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Question

Two coherent sources A and B are in phase and form the endpoints of the diameter of a semicircle with AB = 6λ. An observer moves along the open semicircular arc joining A and B. How many positions of minimum intensity occur on the arc?

Physics · Wave Optics · interferece of light and huygen principle

G1 Physics · Accepted Answer

For minima, Δ = (n+1 ÷ 2)λ. The allowed signed values on the open arc are ±0.5λ, ±1.5λ, ±2.5λ, ±3.5λ, ±4.5λ, ±5.5λ. There are 12 such values, each corresponding to one point on the arc. Hence the answer is 12.