Comparing Energy Transmitted by Light & Sound: Help Needed!

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Discussion Overview

The discussion revolves around comparing the energy transmitted by light waves and sound waves. Participants explore the theoretical frameworks and equations related to energy in both types of waves, as well as the challenges in making direct comparisons due to their differing natures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that the energy of a light wave is determined by the frequency of the photon, as expressed by the equation E=hf, and inquires if a similar equation exists for sound waves.
  • Another participant expresses skepticism about the feasibility of comparing the energies of light and sound due to their fundamentally different characteristics.
  • A participant questions whether the energy of light waves is generally much higher than that of sound waves, suggesting this comparison would be useful.
  • One participant provides equations for energy density and sound intensity, indicating a mathematical approach to understanding sound energy.
  • Another participant challenges the notion that light waves always have higher energy than sound waves, suggesting that both types of waves can vary widely in energy levels depending on their conditions.
  • A later reply discusses the equivalence of energy expressions for photons and phonons in a quantum context, but emphasizes the complexity of comparing classical electromagnetic and acoustic waves, noting that energy depends on both frequency and amplitude.
  • One participant highlights the distinction between classical waves in a medium and quantum waves, indicating that they require different mathematical treatments.

Areas of Agreement / Disagreement

Participants express differing views on the comparability of energy in light and sound waves. While some suggest that a comparison could be made, others argue that the differences in wave characteristics complicate direct comparisons. No consensus is reached on whether light waves inherently possess higher energy than sound waves.

Contextual Notes

The discussion reveals limitations in the assumptions made about energy comparisons, particularly regarding the dependence on frequency and amplitude, as well as the differing mathematical frameworks required for classical and quantum wave descriptions.

macman83
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I am aware that the energy of a light wave is dependent 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
 
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I'm not so sure you can readily compare the energies.
They are very different waves
 
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?
 
Try these definitions. You will need to look up the units for yourself.

[tex]EnergyDensity = \frac{{\Pr essur{e^2}}}{{density\;x\;velocit{y^2}}} = \frac{{{P^2}}}{{\rho {c^2}}}[/tex]

[tex]SoundIntensity = rate\;of\;energy\;transfer = \frac{{{P^2}}}{{\rho c}}[/tex]
 
macman83 said:
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.
 
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.
 
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.
 

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