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Intensity of wave source

  1. Aug 14, 2013 #1
    This is something I don't relly get. I keep reading that the intensity of a wave is proportional to the square of its amplitude.

    So let's suppose we have a random wave source, with amplitude A0. If we replace that source with five identical copies of it, their collective amplitude is 5A, yes? But have I really raised the energy level at the source by a factor of 25? What am I missing here?
  2. jcsd
  3. Aug 14, 2013 #2


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    Are you assuming that the 5 identical sources are located in exactly the same spot (superimposed on one another)? If so, then I believe the total energy radiated by the sources would be 25 times greater than one source alone.

    Think about the special case where the source is just a single charge q oscillating in simple harmonic motion . Superimposing 5 such oscillators is simply equivalent to increasing the charge from q to 5q. The power radiated by an oscillating charge is proportional to the square of the charge. So, the energy radiated with 5q is 25 times that of q.

    If the 5 oscillators do not oscillate in phase, but have randomly changing phase shifts relative to one another, then I believe the average radiated power output would be just 5 times that of one oscillator.
  4. Aug 14, 2013 #3


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    How do intensity, amplitude, and power all relate to each other in this context?
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