Comparing Energy Transmitted by Light & Sound: Help Needed!

[macman83]

I am aware that the energy of a light wave is dependant solely on the frequency of the incident photon according to E=hf
Is there a similar equation for sound waves to work out the energy transmitted?

If not does anyone have a suggestion on how to compare the energies transmitted by light and sound??
Hope you can help as I'm really struggling to find this info :D

Thanks in advance
Mark

 

[dacruick]

I'm not so sure you can readily compare the energies.
They are very different waves

 

[macman83]

shame it would have been handy to be able to compare.
Am i correct in saying that the energy of a light wave is likely to be much higher than that of a sound wave?

 

[Studiot]

Try these definitions. You will need to look up the units for yourself.

$$EnergyDensity = \frac{{\Pr essur{e^2}}}{{density\;x\;velocit{y^2}}} = \frac{{{P^2}}}{{\rho {c^2}}}$$

$$SoundIntensity = rate\;of\;energy\;transfer = \frac{{{P^2}}}{{\rho c}}$$

 

[dacruick]

shame it would have been handy to be able to compare.
Am i correct in saying that the energy of a light wave is likely to be much higher than that of a sound wave?

I'm not so sure...I would have to say no though. You could figure it out with a few equations off of wikipedia most likely.

You would have to generalize a light wave and a sound wave first though. Technically both of the waves could be really high energy, and really low energy.

 

[Bill_K]

If you're comparing a single quantum, then they're exactly the same: E = hω for the photon and E = hω for the phonon. Only difference is that ω=ck for the photon and ω=ω(k) for the phonon (dispersion).

But I think what you really have in mind is a classical situation, and you want to compare an electromagnetic wave on one hand to an acoustic wave on the other. And in that case, there's no answer -- the energy in the wave depends not only on the frequency but also the amplitude. A sound can have a greater energy density than a light wave if the sound is loud and the light is dim. Or vice versa.

 

[Drakkith]

The classical wave in a medium, while having some relation to the quantum wave, is a very different effect. A wave in water or air is the collective motion of a large amount of particles. The quantum wave describes one single particle at a time. So, while similar, the two are very different and require different math.