# Amplitude and frequency dependence on energy of a wave.

1. Aug 21, 2013

### Famwoor2

Hello all,

I have learned that the energy of a wave is proportional to the square of its amplitude. I have also learned (by the Planck relation) that the energy of a wave is proportional to the frequency of the wave. Doesn't this imply that the frequency of a wave is proportional to the square of its amplitude? I know this deduction is wrong; what am I messing up here??

Thanks for your help and time,
F2

2. Aug 21, 2013

### Jolb

The energy of a photon is proportional to its frequency. Eγ=hv where h is Planck's constant and v is the frequency.

The energy of an EM wave is indeed proportional to the square of its amplitude. But this wave is made of many individual photons. An EM wave coming from a blue light can have the same energy as an EM wave coming from a red light, but the red light will consist of more photons to make up for a smaller energy per photon.

3. Aug 21, 2013

### Famwoor2

So is a photon a wave packet, and an EM wave a composition of wave packets (photons)?

4. Aug 21, 2013

### davenn

Hi Famwood2

that's my understanding, Yes tho through reading I understand that a photon doesn't have to be restricted to a wave packet

here's a couple of articles you may find interesting

Photon wave functions, wave-packet quantization of light, and coherence theory
http://arxiv.org/ftp/arxiv/papers/0708/0708.0831.pdf

Focus: Shaping Single Photons
Published September 5, 2008 | Phys. Rev. Focus 22, 8 (2008) | DOI: 10.1103/PhysRevFocus.22.8

cheers
Dave

5. Aug 21, 2013

Thanks!