Constructive interference occurs when the path difference between two coherent waves is

  • A. an odd number of half wavelengths
  • B. a whole number of wavelengths
  • C. always zero
  • D. one quarter of a wavelength

Explanation

A path difference of a whole number of wavelengths brings the waves back into phase, so the crests coincide and the amplitude is a maximum. An odd number of half wavelengths puts them in antiphase and gives destructive interference. Zero path difference is simply the special case of the central maximum.

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