Understanding Wave Energy: Amplitude vs Frequency

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Discussion Overview

The discussion revolves around the relationship between wave energy, amplitude, and frequency, exploring how these factors determine the energy of various types of waves, including classical waves and electromagnetic waves. The scope includes theoretical considerations and conceptual clarifications regarding different wave types.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the energy of a wave is proportional to the amplitude squared for most physical waves, including water and sound waves.
  • Others argue that for photons, which are massless particles, energy is proportional to frequency, as described by the equation E=h freq, where h is Planck's constant.
  • A participant notes that the relationship between frequency and energy in quantum mechanics is counterintuitive and highlights the probabilistic nature of photon amplitude.
  • One participant questions whether electromagnetic (EM) waves and photons are fundamentally the same, suggesting that the energy of EM waves should also depend on frequency.
  • Another participant clarifies that while classical wave energy is determined by amplitude, the density of photons in an EM wave is influenced by frequency, with lower frequencies corresponding to a greater number of photons for a given amplitude.
  • It is mentioned that for sound waves, the power transported is proportional to both the squared amplitude and squared frequency, while for water waves, the relationship is more complex but can also involve squared amplitude and frequency.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between amplitude and frequency in determining wave energy, with some asserting that amplitude is the primary factor for classical waves, while others emphasize the role of frequency in the context of photons and electromagnetic waves. The discussion remains unresolved regarding the interplay between these factors across different wave types.

Contextual Notes

Limitations include the dependence on definitions of wave types and the complexity of relationships in different contexts, such as classical versus quantum mechanics. Some mathematical relationships are not fully explored or resolved.

IMGOOD
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I am just really confused about what determines energy of a wave?! I have heard that the energy of a wave is proportional to the amplitude squared but I have also heard that frequency determines a wave's energy. Which is the correct answer? Can they both be true?
 
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Classically, it is just the amplitude. You're probably confusing this with photons, which have frequency proportional to their energy.
 
Amplitude squared for almost all physical waves- water, pressure, electromagnetic etc.

For photons however, which are massless particles, the energy is proportional to the frequency, with the proportionality constant h (planck's constant)

E=h freq

You have to be Einstein to discover things like that- and in fact he did. He deduced the above relation from the 'photo-electric effect'.

It's completely counterintuitive that frequency should have anything to do with the energy of the wave, but that's what quantum-mechanics gives.

Edit: And even more weird: The amplitude squared for photon quantum waves is the probability that the photon is found in that place when a measurement is made.

Nobody understands that one- but it seems to be how the universe works.
 
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Isn't that the same thing? I mean, aren't EM waves composed of photons (or rather they are one and the same thing) and therefore whatever determines the energy of a photon would also determine the energy of the EM waves (i.e the frequency)?
 
The energy of *any* classical wave is determined by the amplitude. If you want to describe an EM wave in terms of photons, given a particular amplitude (and hence total energy), the number of photons composing the wave is greater if the frequency is low. You should think of frequency (or perhaps more suggestively, wavelength) as determining the density of photons in an EM wave.
 
cesiumfrog said:
The energy of *any* classical wave is determined by the amplitude. If you want to describe an EM wave in terms of photons, given a particular amplitude (and hence total energy), the number of photons composing the wave is greater if the frequency is low. You should think of frequency (or perhaps more suggestively, wavelength) as determining the density of photons in an EM wave.
I see. That makes a lot of sense and it is a pretty nice way to look at the relationship between photons and EM waves. Thanks! :smile:
 
For sound waves (including seismic waves) power transported is proportional to the squared amplitude times the squared frequency.
For water waves the dependence is more complex, but is some cases it is also proportional to the squared amplitude and squared frequency.
 

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