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Not really a homework question per se, but i am just curious about this:

Energy of a wave is given by the planck relation, which should be proportional to its frequency.

However in electrical engineering we always learn that the energy of a wave is the square of its magnitude; nothing to do with frequency.

So are these 2 concepts equivalent?

Thanks.

John Tan
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2 Answers2

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The energy of a photon is $h\nu$, but that's the energy of an individual photon, not of the whole wave. The wave coming from, for example, your laser is made up from multiple photons and if you add up all the energies of the individual photons you'll get the total energy of the wave.

John Rennie
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Good topic, energy of the wave does not depend on frequency only if you consider single bump of the wave, then YES its only about amplitude, otherwise total energy of the wave packet has to depend on the frequency (number of bumps per time). So in quantum physics you can think of the wave amplitude as being FIXED, then everything has to depend on the frequency of the wave packet -- we need energy per time.

Asphir Dom
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