One beam of coherent light travels path p1 in arriving at point q and another coherent beam travels path p2 in arriving at the same point. if these two beams are to interfere destructively, the path difference p1 - p2 must be equal to one beam of coherent light travels path p1 in arriving at point q and another coherent beam travels path p2 in arriving at the same point. if these two beams are to interfere destructively, the path difference p1 - p2 must be equal to an even number of half-wavelengths. a whole number of half-wavelengths. a whole number of wavelengths. zero. an odd number of half-wavelengths.

an odd number of half-wavelengths.

Explanation:

For two coherent beams to interfere destructively

path difference must be equal to odd multiple of half wave-length . Or

path difference P₁ - P₂  = ( 2n+1) λ /2

where  λ is wave length of coherent light. Only then the crest of one will fall upon trough of the other light. Here the word crest and trough have been used symbolically to represent region of opposite phased of light waves.

dopamine..

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small = small current large mag large current