Two coherent point sources A and B emit in phase and are separated by a distance 3.6λ. Consider only points lying strictly between A and B on the straight line joining the sources. How many points of maximum intensity occur between the sources?
Physics · Wave Optics · interferece of light and huygen principle
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Question

Two coherent point sources A and B emit in phase and are separated by a distance 3.6λ. Consider only points lying strictly between A and B on the straight line joining the sources. How many points of maximum intensity occur between the sources?

Physics · Wave Optics · interferece of light and huygen principle

G1 Physics · Accepted Answer

Let O be the midpoint and let P be at distance x from O along AB. Between the sources, Δ = 2|x|. Thus Δ varies from 0 to 3.6λ. For maxima, Δ = nλ. Allowed n values are 0, 1, 2, 3. The n = 0 maximum occurs once at O. Each non-zero n gives two symmetric positions. Therefore, number of maxima = 1+2×3 = 7. Hence the answer is 7.