Basic physics question (frequency/energy relation)

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Discussion Overview

The discussion revolves around the relationship between frequency and energy in different contexts, particularly in sound and light, and how these concepts apply when a medium is involved. Participants explore theoretical implications, practical examples, and the complexities of wave behavior in various media.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that higher frequency correlates with higher energy, but question why lower frequencies seem to penetrate media more effectively.
  • Examples from sound and light are provided, such as the perception of bass sounds and the color of sunlight at different times of day, to illustrate the phenomenon.
  • One participant introduces water waves to discuss how lower frequency waves can affect water levels more gradually, allowing for different interactions with structures like breakwaters.
  • Another participant challenges the generalization that lower frequencies always transmit better, citing examples where higher frequencies can penetrate certain materials more effectively.
  • Concerns are raised about the relationship between frequency, amplitude, and energy, particularly in the context of sound waves versus quantized electromagnetic waves.
  • The equation E = hf is referenced to clarify the energy of photons in relation to frequency, but the distinction between energy and amplitude in wave behavior is emphasized.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between frequency and energy, with no consensus reached. Some argue for a straightforward correlation, while others highlight complexities and exceptions in various contexts.

Contextual Notes

Limitations include the dependence on specific media and conditions, as well as unresolved aspects of wave behavior in relation to amplitude and frequency. The discussion does not resolve the complexities of energy transmission across different wave types.

SoPM
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I almost feel embarrassed to ask this. I've always understood it to be that the higher the frequency, the higher the energy (at least from what I've been taught). However, something has always bugged me: why then, when a medium is involved, are the lower frequencies the ones that make it through? Wouldn't this mean that the lower frequencies have more energy to perturb that medium?

Examples of what I mean,
Sound: If someone is blasting music in their car, or you walk outside past a night club, you hear the bass (lower frequency).

Light: At sunrise/sunset, the sun looks yellow/gold because it has to travel through more atmosphere, deflecting the higher frequencies and only the lower frequencies (orange, yellow) reach you eyes.

Perhaps this has to do with resonant frequencies but I'm not sure. Could someone explain the relationship between frequency and energy that explains this?
 
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Consider water waves. It's easy to build a breakwater that will protect a harbor against the highly energetic waves that a storm drives in - these smash excitingly and energetically against the breakwater, throwing spouts of white water many meters into the sky with every peak in amplitiude. But compare with the low-energy, low frequency (twelve hours!), long wavelength (halfway around the earth!) wave represented by the tides... these drift gently in, passing the breakwater as quietly as they pass any other random piece of topography along the coast, and over a period of hours they move the water level in the harbor by their full amplitude.

Intuitively, what's going on here is that the lower-frequency wave is changing the height of the water more slowly so that the water level has time to adjust and the next increase in height will build on the previous one. The higher-frequency storm wave piles water up against the breakwater, but before the water has time to flow on into the harbor the next trough has come along.
 
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First, your statement that "the lower frequencies are the the ones that makes it through" is a generalization without support.
Metals are opaque to visible but transparent in UV and some bands in x-rays. Just one example that contradict this statement.
Transmission coefficient of EM waves is a complicated function of wavelengths and you cannot make any general statements, valid for any material and spectral range.
Air scatters more blues than red due to the size of the scattering centers rather than the energy of the radiation. It is valid when the model of Rayleigh scattering is applicable.
You can have a medium that scatters more lower frequencies than higher frequencies.

And second, the statement that higher frequency waves have more energy than lower frequency waves makes sense for quantised waves, like the EM waves. It just means that a quanta has more energy at higher frequencies.
In the case of sound waves described by a continuous model, what would this mean? A tsunami wave with amplitude of tens of meters will have less energy than an ultrasound beam used for medical imaging? The energy of the wave itself depends on both amplitude and frequency.
 
If you refer to the equation
E =hf,
that relates the energy of photons to their frequency. It doesn't relate to the amplitude of a wave, which (squared) relates to the Power density. The number of photons for a given power will relate to individual photon energy.
Linking this to the behaviour of mechanical (water) waves is a big step. Is all that not more related to matching of the different wavelengths to the structures involved and propagation losses of surface water waves?
 

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