Energy in waves (Amplitude and Frequency)

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Discussion Overview

The discussion revolves around the relationship between energy, amplitude, and frequency in both mechanical and electromagnetic waves. Participants explore whether energy is proportional to amplitude squared in mechanical waves and how this concept applies to electromagnetic waves, particularly in the context of the photoelectric effect.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that in mechanical waves, energy is proportional to the square of the amplitude (E = kA^2) and question the nature of the constant k.
  • Others argue that in electromagnetic waves, energy is proportional to frequency (E = hf), suggesting that amplitude does not play a role in determining energy.
  • A participant raises the question of whether amplitude has any meaning for a photon, leading to discussions about the relationship between photons and electromagnetic waves.
  • There is a suggestion that amplitude in the context of electromagnetic waves may represent the density of particles, with each particle having a minimum measurable amplitude.
  • Some participants express uncertainty about whether an electromagnetic wave should be considered as a collection of photons or as a single entity.
  • One participant states that the photoelectric effect implies that energy is not proportional to amplitude but rather to frequency, prompting further exploration of this concept.
  • Another participant mentions that the change in wavelength affects the energy of an electromagnetic wave, indicating a relationship between frequency and energy.
  • There is a request for clarification on the value of k and whether it varies with materials, with some suggesting that k could be related to frequency.

Areas of Agreement / Disagreement

Participants express differing views on the role of amplitude in electromagnetic waves and its relationship to energy. While some agree that energy in electromagnetic waves is primarily determined by frequency, others challenge this perspective, leading to an unresolved discussion on the implications of the photoelectric effect and the nature of photons.

Contextual Notes

Participants highlight the distinction between wavelength and amplitude, and there are mentions of the complexities involved in determining energy transfer through different materials, particularly in mechanical waves.

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---------- About Mechanics waves ---------

We know that in mechanics waves, energy is proportion to Amplitude^2.
So we can write equation as E = kA^2 , where k is a constant.

Is it possible to find this constant (k) ?
Is k different in other waves (meaning it is depended on other values) or it is constant to all mechanics waves ?

---------- About Electromagnetics waves ---------

Does "Energy proportion to Amplitude^2" also apllied to ElectroMagnetics waves ?

Is the result of photoelectric effect meaning that energy of EM waves is not proportion to amplitude but only frequency ?

Will the calculation be accurated if I calculate energy from Amplitude^2 in EM waves ?

Thank in advance.
 
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Does amplitude have any meaning for a photon?
 
Dr_Morbius said:
In electromagnetic waves the energy is proportional to the frequency, E=hf.

http://en.wikipedia.org/wiki/Electromagnetic_radiation

h taking the place of A^2 as the smallest measurable density.

The energy of any wave is proportional to the product of the density(amplitude) and the frequency.
 
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LostConjugate said:
h taking the place of A^2 as the smallest measurable density.

The energy of any wave is proportional to the product of the density(amplitude) and the frequency.

Yes but for an EM wave does that mean that the amplitude is always set to a certain value?
 
Drakkith said:
Yes but for an EM wave does that mean that the amplitude is always set to a certain value?

No, not at all. The particle view attempts to break down the EM wave into a collection of particles. The Amplitude is now the density of particles, each particle having the minimum measurable amplitude and only differing in frequency.

It is just a point of view.
 
LostConjugate said:
No, not at all. The particle view attempts to break down the EM wave into a collection of particles. The Amplitude is now the density of particles, each particle having the minimum measurable amplitude and only differing in frequency.

It is just a point of view.

So the amplitude of a single photon is set then?
 
Drakkith said:
Hold on, are you talking about a collection of photons or about just one?

I was talking about a collection of photons, that is what an EM wave is right?
 
Drakkith said:
So the amplitude of a single photon is set then?

Yup, it is the smallest measurable amplitude of an EM wave. Plank's constant
 
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  • #10
LostConjugate said:
I was talking about a collection of photons, that is what an EM wave is right?

Not really. An EM wave to me means a photon. But I could be incorrect.

LostConjugate said:
Yup, it is the smallest measurable amplitude of an EM wave. Plank's constant

Ok, so Planks constant, AKA the amplitude, helps defines the energy of a particle because a higher frequency would have more waves per second, more peaks or whatever?
 
  • #11
Drakkith said:
Not really.



Ok, so Planks constant, AKA the amplitude, helps defines the energy of a particle because a higher frequency would have more waves per second, more peaks or whatever?

The frequency is the velocity of the source charge, or the rate of change of the wave function. Combine this with the amplitude^2 to get your energy.

In the particle view, the particles have the lowest measurable amplitude, empirically found to be plank's constant.
 
  • #12
Drakkith said:
Not really. An EM wave to me means a photon. But I could be incorrect.

A photon is the quanta of an EM wave.

Edit: it is nothing like a wave.
 
  • #13
LostConjugate said:
A photon is the quanta of an EM wave.

Edit: it is nothing like a wave.

Hrmm. I am unsure about this. A photon is quantized, but I think that the photon IS the EM wave.
 
  • #14
Thank everyone.

DarkDrag0nite said:
Is the result of photoelectric effect meaning that energy of EM waves is not proportion to amplitude but only frequency ?

But I think I am missing some important point of Photoelectric effect. Isn't that means amplitude is not proportion to energy ?
 
  • #15
DarkDrag0nite said:
Thank everyone.



But I think I am missing some important point of Photoelectric effect. Isn't that means amplitude is not proportion to energy ?

That is correct. The change in wavelength determines the amount of change in energy of an EM wave. (Photon) Double the frequency (half the wavelength) and you double the energy.
 
  • #16
somebody tell me what is the value of "k".
It is constant (or) varies with materials?
 
  • #17
Drakkith said:
That is correct. The change in wavelength determines the amount of change in energy of an EM wave. (Photon) Double the frequency (half the wavelength) and you double the energy.

Anyway, Wavelength and Amplitude are different.
 
  • #18
maruthisarat said:
somebody tell me what is the value of "k".
It is constant (or) varies with materials?

k would be your frequency. The material is not usually taken into account with mechanical waves when determining the energy transferred through the material, it is usually taken to be some material that is good at transferring energy. If you want to look into inefficiencies in the material first you take the mechanical wave energy and then you apply inefficiencies in some complex manner.
 
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