What is the Frequency of a Photon? Understanding Light Particles Explained

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Discussion Overview

The discussion revolves around the concept of the frequency of a photon, exploring its implications in the context of wave-particle duality, quantum mechanics, and the historical understanding of light. Participants question the nature of frequency as it relates to photons, which are typically considered particles, and seek clarification on what is being measured when discussing photon frequency.

Discussion Character

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

Main Points Raised

  • Some participants express confusion about the concept of frequency in relation to photons, questioning whether it is appropriate to attribute a wave characteristic to a particle.
  • One participant mentions that frequency is related to the energy of a photon through the equation E = hf, where h is Planck's constant.
  • Another participant discusses the historical context of light being viewed as a wave and the transition to understanding it as quantized energy packets, referencing Planck and Einstein's contributions.
  • A participant argues that the term "length of a photon" is misleading, asserting that photons are massless point-like particles and that the velocity of light was measured rather than discovered.
  • There is a discussion about the distinction between wavelength and the concept of "length" of a photon, with some participants asserting that frequency is a measure of oscillation in the electromagnetic field.
  • One participant mentions that particles, including electrons, possess frequency and wavelength, referencing electron diffraction as an example.
  • Another participant introduces de Broglie's hypothesis of matter waves, suggesting that all particles exhibit wave-like behavior.

Areas of Agreement / Disagreement

Participants generally express differing views on the relationship between frequency and photons, with some asserting that frequency is a wave property applicable to photons, while others challenge the terminology and concepts used. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

There are unresolved distinctions between terms like "length" and "wavelength" in the context of photons, as well as varying interpretations of historical developments in the understanding of light and quantum mechanics. The discussion reflects a mix of conceptual and technical challenges without a clear consensus.

madness
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Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
Thanks guys
 
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madness said:
Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
Thanks guys

Good question. I would like also to know what is, really, the quantum momentum of a particle.

TI.
 
Well,if you had read about blackbox radiation and Planck's 1900 analysis,you'd have gotten the right idea.

Daniel.
 
madness said:
Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
Thanks guys
We're measuring the photon's energy which is related to the frequency of the wave by E = hf, where h = Planck's constant.
 
madness said:
Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
Thanks guys

Light was previously considered to be a wave, since it bends arround corners and give interferrence patterns etc. Then people meassured black body radiation and Planck discovered that things work better if energy comes in packets, aslo einstein used this energy in packets idea to explain the photo electric effect. Nowadays things are considered to obey the laws of quantum mechanics and thus all has frequency and so on..
 
Hi madness,
Only the length of a photon has been known since the rainbow was analyzed a couple of centuries ago. Then when the velocity of light was discovered a century ago someone divided the distance traveled by a photon in one second by the length of the photon and called it "frequency" rather than the number of unitary photons per second. Go figure. Jim
 
NEOclassic said:
Hi madness,
Only the length of a photon has been known since the rainbow was analyzed a couple of centuries ago. Then when the velocity of light was discovered a century ago someone divided the distance traveled by a photon in one second by the length of the photon and called it "frequency" rather than the number of unitary photons per second. Go figure. Jim

Say what ?What length of the photon...?The photon is a masless pointlike particle.

The velocity of light was not discovered,but measured by Bradley,Ro/mer,Fizeau etc.

Daniel.
 
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dextercioby said:
Say what ?What length of the photon...?The photon is a masless pointlike particle.

The velocity of light was not dicovered by measured by Bradley,Ro/mer,Fizeau etc.

Daniel.

Is it the policy of this forum to allow people to continually write nonsense in a confident fashion? (Not referring to you, of course, Daniel).
 
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juvenal said:
Is it the policy of this forum to allow people to continually write nonsense in a confident fashion? (Not referring to you, of course, Daniel).
Hi juvenal,

When someone signs up to becoming a PF member, the agree to abide by certain guidelines (freely available on the PF website).

Writing nonsense is not against the guidelines, nor is confidence in how one writes a post - we do not wish, in any way, to restrict free enquiry ... initially. If a PF member wishes/chooses to remain ignorant, and continue to ask questions that have been answered before (even if they're from the same member!), so be it.

OTOH, if they continue to confidently post nonsense (not questions), we hope that other PF members will report such behaviour; one or more moderators will then review the relevant posts, and take whatever actions may be appropriate.

I hope this clarifies things for you.

Kind Regards
Nereid
 
  • #10
Hi Daniel and juvy (and I don't mean you Daniel),
The length of a QM Sodium D yellow photon is 5,890 Angstroms(10^-10 meters) and there are literally many many different spectral photons and not one is a point particle. Oh yes' forgive me! - photons were never discovered they were just measured without having been discovered. Cheers, Jim
 
  • #11
That's the WAVELENGTH of the radiation emitted by sodium.

Photons are points particles.

Daniel.
 
  • #12
NEOclassic said:
Hi madness,
Only the length of a photon has been known since the rainbow was analyzed a couple of centuries ago. Then when the velocity of light was discovered a century ago someone divided the distance traveled by a photon in one second by the length of the photon and called it "frequency" rather than the number of unitary photons per second. Go figure. Jim

Let me waste some of my time then:

You might be talking about wavelength and not length. These are two different things. The wavelength of a moving bowling ball, for example, according to quantum mechanics, is not the same as the the length of a bowling ball.

Even so, the distance traveled by a photon in one second is approx 3E+08m. You divide by the wavelength of the photon, and you get a unitless number. Frequency is in units of Hz which have units of inverse seconds.
 
  • #13
madness said:
So what is it that we are actually measuring when we talk about the frequency of a photon?

The number of times the electromagnetic field oscillates per second. This determines the diffractive properties of light, as well as how the light will behave when traveling through certain media.

madness said:
Isn't frequency an attribute that we would generally associate with waves rather than particles

Nope, particles (e.g. electrons) also posess a frequency and wavelength (Look up electron diffraction).

Claude.
 
  • #14
From post # 13 (lucky number,i guess) "Isn't frequency an attribute that we would generally associate with waves rather than particles" (by madness)
"Nope, particles (e.g. electrons) also posess a frequency and wavelength (Look up electron diffraction)." (by Claude Bile)

Funny,electron diffraction is properly explained in terms of de Broglie pilot waves (or if u prefer Schrödinger scalar waves),where the "k","\lambda" have the same significance as for an em wave in Maxwell's theory. :rolleyes:

Daniel.
 
  • #15
Terra Incognita said:
Good question. I would like also to know what is, really, the quantum momentum of a particle.

TI.

De Broglie postulated matter waves, according to him, all particles must behave as waves and vice versa, an idea resulting from Einstein's concept of a light photon.
The wavelength is given by
l=h/mv
Macroscopic particles have too large momentum as compared to Planck's constant(6.6*10^-36).
 
  • #16
madness said:
Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
Thanks guys

The photon frequency is the wave frequency, no problem with it. A single photon is a sufficiently long wave packet (of thousands or dozens thousands of vibrations in it). So we safely speak of its frequency. Now everything, everything is waves with the following time dependence: exp(-iEt/ћ). While interaction, the initial and final states of interacting "particles" are written in QM as a product of wave functions, in particular:exp(-iE1t/ћ)*exp(-iE2t/ћ)=exp(-i(E1+E2)t/ћ). You see, the energies are added as if the waves were possessing particle energies E1 and E2. Photon is not exclusion. Photon energy and photon frequency is nearly the same thing (they are proportional to each other). That is how the wave-particle duality works in QM. Again, everytbing is a wave.
 
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  • #17
Bob_for_short said:
The photon frequency is the wave frequency, no problem with it. A single photon is a sufficiently long wave packet (of thousands or dozens thousands of vibrations in it). So we safely speak of its frequency. Now everything, everything is waves with the following time dependence: exp(-iEt/ћ). While interaction, the initial and final states of interacting "particles" is written in QM as a product of wave functions, in particular:exp(-iE1t/ћ)*exp(-iE2t/ћ)=exp(-i(E1+E2)t/ћ). You see, the energies are added as if the waves were possessing particle energies E1 and E2. Photon is not exclusion. Photon energy and photon frequency is nearly the same thing (they are proportional to each other). That is how the wave-particle duality works in QM. Again, everytbing is a wave.

this is a 4 year old thread...
 
  • #18
malawi_glenn said:
this is a 4 year old thread...

Yes, indeed...
 
  • #19
@ juvenal; I don't mean to troll this thread on too long with questions, but I had a bit of a misconception also and I thought the bowling ball analogy was a pretty good one. So just to be clear with what I have read so far- considering a single photon to be the bowling ball- is the frequency of the bowling ball implying the movement of the bowling ball sort of shaking or "vibrating in place" even as it is headed toward the end of the lane? (like a wobbling bullet headed towards it's target) I guess a better example would be throwing a phone on constant vibrate down a hallway. Is that what the frequency of a photon is describing?
 
  • #20
oh god, it is old. well, if anyone can answer my previous question, many thanks
 
  • #21
Woah - it lurches back to life!
@mAMBOkING: did you ever work out the answer?
is the frequency of the bowling ball [as photon] implying the movement of the bowling ball sort of shaking or "vibrating in place" even as it is headed toward the end of the lane
... no.

Note: it is valid to add to an old thread - if I got here googling a question then others may also. We ask and answer these questions in a public forum in the hope that others will benefit from the discussion later as well as to satisfy ourselves.

If anyone knows a better thread elsewhere - it would be a good idea to append the link to this one and get a mod to close up.
 

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