Two coherent point sources A and B are in phase and are separated by 3.6λ. A circular observation path is centred at the midpoint of AB and encloses both sources. How many positions of minimum intensity are encountered during one complete revolution of the observer?
Physics · Wave Optics · interferece of light and huygen principle
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Question

Two coherent point sources A and B are in phase and are separated by 3.6λ. A circular observation path is centred at the midpoint of AB and encloses both sources. How many positions of minimum intensity are encountered during one complete revolution of the observer?

Physics · Wave Optics · interferece of light and huygen principle

G1 Physics · Accepted Answer

For minima, Δ = (n+1 ÷ 2)λ. Allowed signed values satisfying |Δ| < 3.6λ are ±0.5λ, ±1.5λ, ±2.5λ, ±3.5λ. This gives eight signed values. Each corresponds to two points on the circle. Hence, number of minima = 8×2 = 16. Therefore the answer is 16.