Two coherent in-phase sources are separated by exactly 5λ. An observer moves once around a circular path centred at the midpoint of the sources and enclosing both sources. How many positions of minimum intensity are encountered?
Physics · Wave Optics · interferece of light and huygen principle
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Question

Two coherent in-phase sources are separated by exactly 5λ. An observer moves once around a circular path centred at the midpoint of the sources and enclosing both sources. How many positions of minimum intensity are encountered?

Physics · Wave Optics · interferece of light and huygen principle

G1 Physics · Accepted Answer

For minima, Δ = (n+1 ÷ 2)λ. Allowed signed values are ±0.5λ, ±1.5λ, ±2.5λ, ±3.5λ, ±4.5λ. There are ten signed values. Each occurs at two points on the circle. Therefore, number of minima = 10×2 = 20. Hence the answer is 20.