# Amplitude vs Energy

1. Sep 19, 2011

### jaumzaum

Is there a equation that calculate the energy of a wave acccording to the amplitude

Another question, The plank equation E = h.f calculate the energy of any wave according to the frequency? If so, why doesn't the amplitude affect the energy (in the equation)?

2. Sep 19, 2011

### Drakkith

Staff Emeritus
Plank's equation is only applicable to an Electromagnetic wave. IE Light. It was discovered that the energy per "wave" was only related to frequency of the light. As for WHY amplitude doesn't matter, that is complicated and beyond my knowledge.

3. Sep 19, 2011

### Freeze3018

Einstein's showed that (in his 1905 papers) light is made up of photons and each photon's energy depends on its frequency.
energy of 1 photon is h.f

4. Sep 20, 2011

### nasu

There are various formulas, depending on the type of the wave (EM, sound, etc). The "energy of the wave" is not a very well defined quantity. You may want to look at energy density, the energy in a specific unit volume, if it's a standing wave. Or maybe the energy flux, the energy transported by a progressive wave through a specific area in unit time.
In general these quantities depend on both the amplitude of the wave and frequency.

Now going to the quantum picture, the Plank formula gives the minimum energy (photon) that the wave may transport, exchange, etc. The total energy density or flux depends on the number of photons in the wave which can be related to the (classical) amplitude of the wave.