Sustained interference patterns

    In order to produce a sustained interference pattern by light waves from multiple sources, which of the following conditions is sufficient?

    a. the sources are coherent
    b. the sources are monochromatic
    c. no more than two sources are allowed
    d. three or more sources are required
    e. none of the choices above are valid

    3. The attempt at a solution

    This question seems messed up to me. From what I understand, both A and B can be correct. I am totally confused. please help if you can, thanks.
  2. jcsd
  3. any help? my brain is melting.
  4. The sources should be coherent.

    The coherent sources, by definition, should possess same wave length, same amplitude and same phase or constant phase difference.

    But a monochromatic source will possess same wave length but not necessarily be of same phase or constant phase difference.

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