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Waves and sound

  1. Jan 14, 2016 #1
    Hi guys. Was studying waves and got a bit confused. Pl help me out.

    Coherent sources are those which produce waves of same frequency, wavelength and velocity. Amplitude need not necessarily be same. Am I right?

    There's another doubt in my mind...

    If two waves produce beats then which of the following quantities are necessarily same for both of them
    Angular wave number( and thus wavelength)
    Angular frequency ( and thus frequecy)
    Velocity of wave

    Please answer only if 100% sure.
  2. jcsd
  3. Jan 14, 2016 #2
    For coherence, they must have the same phase relationship. At least during the coherence time.
    The wavelength depends on frequency and phase velocity so it is not an independent quantity.

    For beats you need to have slightly different frequencies. Amplitudes can be different but then the minims won't be zero.
  4. Jan 15, 2016 #3
    What do you mean by same phase relationship?
    Is my notion about coherent waves correct?
  5. Jan 15, 2016 #4
    So none of these have to be necessarily same for 2 waves to produce beats?
  6. Jan 15, 2016 #5


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    You will not get beats of the two waves are of the same frequency and youdo not move the measuring position or sources; the phase relationship of the two waves stay the same at a given point so the resultant is the same amplitude.
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