Query on constructive interference

Discussion in 'Physics & Math' started by CIEan, Jan 9, 2010.

  1. CIEan Registered Member

    Doing a school paper right now, and would appreciate any answer.

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    I have read in some places that, for two waves, when there is a difference in the path length that is equal to a wavelength, constructive interference will occur. The amplitude of the wave that results is larger than either of the waves that created it—the light will brighten, sound gets louder, etc...

    Does the difference in path length always have to be equal to a wavelength for constructive interference to occur?
    Here the waves have the same wavelength and amplitude, but they are not perfectly parallel to each other:


    Constructive interference can occur in this case?
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  3. kurros Registered Senior Member

    Yes, you're right, constructive interference is occurring in that picture too. The 1 (or any integer) wavelength shift criteria just gives the maximum constructive interference. There is a continuous spectrum between destructive and constructive interference as you vary the phase difference from 1 wavelength (fully constructive) to 1/2 wavelength (fully destructive). Somewhere in the middle you will just get back the same wave, but shifted in phase a little.
    All this is assuming the waves are identical except their phase btw.
    You can consider that constructive/destructive interference just describes what is happening at each particular point along the wave. Two waves can constructively interference in some places and destructively interfere in others.
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