All Photons Move at 300,000km/s.... But Don't?

[arfa brane]

Yes, right, photon's energy is directly proportional to frequency under all circumstances, but can we say that momentum is also directly proportional to frequency under all circumstances...I am afraid, no.

But energy and momentum are related by the expressions $$ \Delta E \Delta t, \Delta p \Delta q $$, where the $$ \Delta $$ conventionally means an interval or range (usually small enough that "locality" makes sense). what is this relation and why do we use it?

Or perhaps you can suggest something more realistic? If you can, what kind of test would it be for the Standard Model, or say, just $$ SU(2) \times U(1) $$ (I guess you have to start somewhere).

P.S. In case you didn't know, I'm being sarcastic. In a very droll, correct sort of way.

 

[James R]

For photons we have $$E=pc$$ and $$E=hf$$. Therefore $$p=hf/c]$$.

It is obvious from this that the photon's momentum is directly proportional to its frequency under all circumstances.

 

[RajeshTrivedi]

Well you can do actually. Anyone familiar with QM will be fully aware that frequency and momentum go hand in hand, related by a simple proportionality factor. Hence the explanation of the uncertainty principle in terms of superposition of waveforms, for example.

As for references here is de Broglie's relation: https://en.wikipedia.org/wiki/Matter_wave

Your reference to De Broglie's matter wave and Uncertainty principle is irrelevant to the point that Photo Electric effect is proportional to momentum or something like that.....Pl see the chronology belowl...

1905 : Einstein Explained the Photo Electric Effect.
1919 : he received the Nobel for this explanation.
1924 : De Broglie proposed matter wave.
1927 : Heisenberg proposed uncertainty principle.

That settles, moreover Einstein did not refer to momentum of photon while explaining Photo Electric Effect, not even in sidelines.

Your insistence with frequency is also not strictly correct, see the rpenner maths even on this thread, the momentum simplified is h/Lambda...as stated by me at the first instances while responding to you.

 

[RajeshTrivedi]

For photons we have $$E=pc$$ and $$E=hf$$. Therefore $$p=hf/c]$$.

It is obvious from this that the photon's momentum is directly proportional to its frequency under all circumstances.

Ref : proof that Photo Electric Effect is not proportional to Momentum of Photon.

The dispute is the linkage or no linkage between Photo Electric Effect and Momentum. My stand is that per say there is no linkage, but some of the members have gone on record stating that Photo Electric Effect is directly proportional to Momentum...

There is no proportionality between between Photo Electric Effect and Momentum.

1. Einstein never referred to momentum of photon while explaining Photo Electric Effect.
2. Concept of 'momentum of photon' is very complex one with few paradoxes (Abraham - Minkowski Controversy)
3. Photon Momentum is actually h/Lambda always but hf/c only in vacuum (Refractive index n = 1)
4. Energy of photon is always hf.
5. the basics of the Photo Electric effect, that the ejection of electron with single photon is possible only if energy of photon is > binding energy of the surface electron. The ensuing electric current with experimental set up completes the effect. So, [(E = hf) > (E0 = hfo)], the balance energy is the kinetic energy of the ejected electron. If E < Eo, then no photo electric effect, this explains the quantum nature of photon as energy bundle.

Now if we say that Photo Electric Effect is proportional to momentum of photon, then at least some parameter of the effect should change by changing the momentum, if change in momentum causes no change in energy of the electron or ensuing current, then we can safely say that momentum of photon plays no role in photo electric effect as being made out by some members...

E = hf (independent of medium)

p = h/Lambda (independent of medium)

say, E > Eo and experiment is conducted in vacuum (or air, approximate), then Photo Electric effect takes place with some residual kinetic energy (E-Eo).

Now change the experimental set up in a medium (with refractive index n), frequency of the light does not change, energy does not change but wavelength changes and momentum changes....but since energy is unchanged there is no change in kinetic energy of the ejected electron.

So, this explains

1. that momentum = hf/c is strictly correct only in vacuum, otherwise h/lambda is ok irrespective of media.
2. There are situations wherein change in momentum makes no impact on Photo Electric effect. The prime condition is that the energy of the incoming photon should be more than the binding energy (work function) of the electron, so it is incorrect to say that Photo Electric Effect is directly proportional to momentum of Photon.

Those who still feel that Photo Electric Effect is directly proportional to momentum of photon, may attempt the same from cause effect analysis, they will get that there is no link, per say. of course as I stated earlier also, many parameters of the photon are interlinked together.

 

[paddoboy]

That settles, moreover Einstein did not refer to momentum of photon while explaining Photo Electric Effect, not even in sidelines.

Only settled in your rather troubled mind Rajesh. I don't believe you have fooled anyone else. Not in the least. Just because Einstein did not mention it does not mean it is wrong.
Einstein was also unaware of BHs.
There is an obvious connection/relationship between speed, momentum, frequency and wave length of light. All depend on one another. Take away the momentum/speed of light and the photelectric effect would not exist.
The properties of light can be explained by the photon model of light that Einstein used to explain said effect.
A photon's energy is proportional to the frequency of the light. All photons of a particular frequency have exactly the same energy. The higher the frequency, the more energetic the photon.
Photons, regardless of their frequency, have zero rest mass and travel at "c" in a vacuum.
Now no matter how much you see the need to twist and squirm, and no matter how many facts you obtain from links with out any reference back to those links, The photoelectric effect would be non existent if light did not have speed/momentum, and if it was not a particle.

 

[paddoboy]

Now if we say that Photo Electric Effect is proportional to momentum of photon, then at least some parameter of the effect should change by changing the momentum, if change in momentum causes no change in energy of the electron or ensuing current, then we can safely say that momentum of photon plays no role in photo electric effect as being made out by some members...

You are hiding behind unreferenced snippets of data that you pinched on the web, while ignoring the overwhelming fact that light/photons have properties that all depend on each other, and the bottom line in those properties is momentum and speed.
Irrespective nothing you have posted without reference, invalidates the fact that everyone has been trying to tell you.

If we get right down to the nitty gritty Rajesh, you started this charade as an act of vengeance or "pay back" for my part in invalidating your BNS.
In this mission of yours so far you have accused me of saying a photon has rest mass, based on me saying in reply to another at post 173....
"I don't believe it is logical to say photons are not moving...How otherwise is the photo electric effect produced".
in reply to BrianHarwarespecialist who inferred that
photons stop moving in their own FoR.
Then quick as a wink, you claim I somehow was inferring a photon had a rest frame from my above statement.
Then you latch on to me again because I said......
That's exactly what I said!
in reply to a post of complicated mathematical rigour by rpenner, after a similar reply by Kittamaru thus.....
Ow wow... that hurt my head lol! Good grief, I'm remembering now why I didn't pursue a math degree!
you replied thus.....
The later statement as made by Rpenner is thoughtful academic statement with sound maths to support, but what you stated in the original was nothing but ignorant rant.
then having lost that one you start on the photoelectric effect and my earlier reply to another......
What has Photo Electric Effect got to do with movement of photon ?? Just to write something on a science forum ??
You would like to correct one more bloomer in above post ? Did you get that ?

You then list a list of names of members whom you claimed I have been less then respectable to. One of those Only Me corrected you and informed you of facts rather than the usual Rajesh inspired fairy tales.
Corrections of your claims and your motives towards me came than from at least three more members.
Then jcc popped into the building and made claims that radiation/light were gravitational waves and that light did not have momentum.
He said in part....
p=m x v, that's momentum
e=h x frequency, is not momentum, just a theory been accepted by some scientists.
without mass, there would be no momentum.
I among others questioned him on the stupidity of that statement and I used solar sails as an example of photon momentum. I said....
Ever heard of solar sails? or light sails?
I wonder how they work if photons have no momentum?
http://www.nasa.gov/mission_pages/tdm/solarsail/#.VYoLWRuqqko
jcc replies....
if that's true, the solar panels on the space station should been pushed by sunlight?
Somehow after correcting jcc on that blooper, you infer that I'm claiming photons have no momentum.
Then you claimed the following after another member berated you for your vendetta and stupidity.......
This is no irony, Kid. This is a pure business decision, economics....
There is a sudden substantial increase in ads traffic on this site, likes of paddoboys are needed, he posts around 25+ posts a day, keeps the ticks on. To him it does not matter whether he is trolling me or Sylwester or OnlyMe or Schemlzer or Q-reeus or Danshaven...he has to just post crap...
Then lo and behold he tries and infers that I'm claiming that light/radiation does not have momentum.

All this just in one thread.
Now rajesh you have some outstanding issues to answer.You have never yet admitted any error of judgement or science.
You have disputed all members on this forum...even those that like you are rather "anti mainstream" have disowned you on the BNS business.
You have disputed numerous professors.
You berate me for supplying links, yet you obviously extract various paragraphs, phrases etc from your own links, never referencing them.
You, as I have just shown, will purposely misinterprete and lie when you are in a corner...Evident in many threads, not just this one.
You as I have shown, are also paranoid particularly when it comes to me.
Perhaps the fact that someone who is a lay person and admits to being a lay person, confronting another lay person, who has problems of delusions of grandeur, is just too much for some to bear.
Finally the question you have sidestepped for more than a week....
You expect we should all ignore what we read from reputable links, what reputable Professors tell us, and what the majority of the forum accepts, in favour of your cosmologically enlightened view. Is that correct?
Give us a yes or a no, and than elaborate if you like.
Don't be shy. It's a genuine concern of a few here I suggest.

Now that I've got all that off my chest, and its all evidenced in this thread, I agree with what at least two or three have already suggested....Time for the cesspool.

 

[arfa brane]

Now change the experimental set up in a medium (with refractive index n), frequency of the light does not change, energy does not change but wavelength changes and momentum changes....but since energy is unchanged there is no change in kinetic energy of the ejected electron.

No, you will have to do a lot better than that. Show me the math. I don't believe at least half of that can be true, so prove it is. Make me look like an idiot.

 

[paddoboy]

stuff up

 

[OnlyMe]

Ref : proof that Photo Electric Effect is not proportional to Momentum of Photon.

The dispute is the linkage or no linkage between Photo Electric Effect and Momentum. My stand is that per say there is no linkage, but some of the members have gone on record stating that Photo Electric Effect is directly proportional to Momentum...

There is no proportionality between between Photo Electric Effect and Momentum.

1. Einstein never referred to momentum of photon while explaining Photo Electric Effect.
2. Concept of 'momentum of photon' is very complex one with few paradoxes (Abraham - Minkowski Controversy)
3. Photon Momentum is actually h/Lambda always but hf/c only in vacuum (Refractive index n = 1)
4. Energy of photon is always hf.
5. the basics of the Photo Electric effect, that the ejection of electron with single photon is possible only if energy of photon is > binding energy of the surface electron. The ensuing electric current with experimental set up completes the effect. So, [(E = hf) > (E0 = hfo)], the balance energy is the kinetic energy of the ejected electron. If E < Eo, then no photo electric effect, this explains the quantum nature of photon as energy bundle.

Now if we say that Photo Electric Effect is proportional to momentum of photon, then at least some parameter of the effect should change by changing the momentum, if change in momentum causes no change in energy of the electron or ensuing current, then we can safely say that momentum of photon plays no role in photo electric effect as being made out by some members...

E = hf (independent of medium)

p = h/Lambda (independent of medium)

say, E > Eo and experiment is conducted in vacuum (or air, approximate), then Photo Electric effect takes place with some residual kinetic energy (E-Eo).

Now change the experimental set up in a medium (with refractive index n), frequency of the light does not change, energy does not change but wavelength changes and momentum changes....but since energy is unchanged there is no change in kinetic energy of the ejected electron.

So, this explains

1. that momentum = hf/c is strictly correct only in vacuum, otherwise h/lambda is ok irrespective of media.
2. There are situations wherein change in momentum makes no impact on Photo Electric effect. The prime condition is that the energy of the incoming photon should be more than the binding energy (work function) of the electron, so it is incorrect to say that Photo Electric Effect is directly proportional to momentum of Photon.

Those who still feel that Photo Electric Effect is directly proportional to momentum of photon, may attempt the same from cause effect analysis, they will get that there is no link, per say. of course as I stated earlier also, many parameters of the photon are interlinked together.

So what you are really saying is that in your mind, when A equals B and C equals B, A does not equal B....

Rajesh, if momentum and frequency can be shown to be proportional.., and the photoelectric effect can be shown to be proportional to either one (momentum or frequency).., then the photoelectric effect must be proportional to both.., the momentum and(/or) frequency of a photon.

I never stop being impressed by how simplistically direct, James puts things....

For photons we have $$E=pc$$ and $$E=hf$$. Therefore $$p=hf/c]$$.

It is obvious from this that the photon's momentum is directly proportional to its frequency under all circumstances.

Stop and think...........

 

[RajeshTrivedi]

So what you are really saying is that in your mind, when A equals B and C equals B, A does not equal B....

Rajesh, if momentum and frequency can be shown to be proportional.., and the photoelectric effect can be shown to be proportional to either one (momentum or frequency).., then the photoelectric effect must be proportional to both.., the momentum and(/or) frequency of a photon.

I never stop being impressed by how simplistically direct, James puts things....



Stop and think...........

1. In medium with (n > 1), for a light photon , wavelength decreases (it gets multiplied by 1/n) and momentum increases (it gets multiplied by n as p = h/lambda), but frequency remains the same and thus the energy also remains same........so the exact relationship is that momentum is inversely proportional to lambda. But if we use frequency the other term refractive index pokes its nose.

2. From the above it can also be made out that even though momentum is changed, but nothing happens to energy (since frequency does not change), so no effect on the kinetic energy (E-Eo if E>Eo) of ejected electron in the process, falsifying the claim that photo electric effect is directly proportional to momentum.


PS: In addition to the chronology given by me in earlier post, it is interesting to note that when Einstein explained the Photo Electric Effect in 1905, the term photon was not there, it was called as quanta of light...and the prevailing concept was that the light propagates as electromagnetic wave but emits or absorbs as the discrete quanta of energy...There could not have been any reference to momentum of photon in 1905..And Einstein explanation of this for which he was given Nobel, still holds. Hope this clarifies.

 

[RajeshTrivedi]

For a free particle in quantum field theory, these relations relate energy, momentum, mass, velocity, frequency, wavenumber and wavelength:

$$E^2 = \left( mc^2 \right)^2 + \left( c \vec{p} \right)^2 \\ E \vec{v} = c^2 \vec{p} \\ E = h f\\ \vec{p} = \frac{h}{2 \pi} \vec{k} \\ | \vec{k} | = \frac{2 \pi}{\lambda} $$


For a massless phenomenon that carries energy and momentum, these equations say:

$$E = c | \vec{p} | = \frac{h c}{2 \pi} | \vec{k} | = \frac{h c}{\lambda} = h f \\ | \vec{v} | = c $$

The conclusion is that Energy, Momentum, Frequency and Wavenumber are all proportional while the magnitude of the velocity is fixed. Massless phenomena which carry energy and momentum travel at the speed of light.

Rpenner in his post #5 gives complete math, which I referred in my response too. The vector momentum equation is h/2pi * k (Pl see his post for clarity) which is simplified as p = hf/c (although he retains more proper and correct form as p = h/Lambda) with an assumption that v = c (for n = 1 only). But in medium of refractive index n > 1 this becomes v = c/n...changing the equations, coupled with the fact that in medium frequency and thus energy (=hf) does not change but wavelength and momentum changes.

 

[exchemist]

So what you are really saying is that in your mind, when A equals B and C equals B, A does not equal B....

Rajesh, if momentum and frequency can be shown to be proportional.., and the photoelectric effect can be shown to be proportional to either one (momentum or frequency).., then the photoelectric effect must be proportional to both.., the momentum and(/or) frequency of a photon.

I never stop being impressed by how simplistically direct, James puts things....



Stop and think...........

There is however an interesting point arising from Rajesh's questioning of the effect of refractive index. Which is nice because it gets us back to the real science we had at the start of this thread. Take a look at this: http://rsta.royalsocietypublishing.org/content/368/1914/927

This implies that in a material medium, a photon has not one but two values for the momentum, a "kinetic" momentum and a "canonical" momentum. This is all rather complicated and seems bound up with the issue of the difference between group and phase velocities in a medium. The message seems to be that, when speaking about either the velocity or the momentum of light in a material medium, one has to be careful what exactly one is referring to.

Interesting, eh?

 

[Dr_Toad]

Very. Thanks for helping me clear up some of my ignorance and confusion on the subject.

 

[paddoboy]

.
PS: In addition to the chronology given by me in earlier post, it is interesting to note that when Einstein explained the Photo Electric Effect in 1905, the term photon was not there, it was called as quanta of light...and the prevailing concept was that the light propagates as electromagnetic wave but emits or absorbs as the discrete quanta of energy...There could not have been any reference to momentum of photon in 1905..And Einstein explanation of this for which he was given Nobel, still holds. Hope this clarifies.

Einstein was not aware of BHs either, at least early in his life.
Your continued references back to Einstein, was the same methodology of our friend Farsight, but that didn't make him automatically correct either.
As I and others have told you, the properties of light like speed, momentum, frequency and wave length are all related and dependant on one another.
That fact goes without saying, and Einstein was not lecturing or addressing lay people like us.

 

[arfa brane]

I'm still trying to get my head around how a change in wavelength isn't a change in frequency.

But this difference between a wave's group and phase velocities is another thing, it means one of them can begin to emerge from a medium before it has fully entered that medium for instance.
What this has to do with the photoelectric effect is another thing I'm still trying to get my head around.

 

[paddoboy]

so it is incorrect to say that Photo Electric Effect is directly proportional to momentum of Photon.

Who has said it is "directly" proportional?

of course as I stated earlier also, many parameters of the photon are interlinked together.

Bingo! And as others have pointed out!
Take away speed and momentum of a photon, and by definition you would not have either a photon or the photoelectric effect.

 

[RajeshTrivedi]

Who has said it is "directly" proportional?

Bingo! And as others have pointed out!
Take away speed and momentum of a photon, and by definition you would not have either a photon or the photoelectric effect.

The horse is dead, Paddoboy. Don't try to beat it any further. It will bring in abuses and sarcasms only, not any science.

However, if you wish to know more about vagaries of Momentum of Photon, jump start with Abraham - Minkowski (Post#484.2) controversy and explore, then you will agree to Feynman that 'light' is difficult nut to crack.

So, that brings me back to Post # 446, just below that enticing still face, Pt#2 and Pt#3 are settled in just 50 posts...try garnering some support against Pt#1, we can run this thread for another 25 posts or so before even Pt#1 is settled. My stand on Pt#1 is unmoved.

 

[paddoboy]

The horse is dead, Paddoboy. Don't try to beat it any further. It will bring in abuses and sarcasms only, not any science.

Sure it is, as well as the other horses you have been beating, including BNS and Schwarzchild radius and gravity overcoming the strong force inside BHs.

However, if you wish to know more about vagaries of Momentum of Photon, jump start with Abraham - Minkowski (Post#484.2) controversy and explore, then you will agree to Feynman that 'light' is difficult nut to crack.

Nice to see you giving credit to a link as a reference. Good stuff!

Abraham - Minkowski
So, that brings me back to Post # 446, just below that enticing still face, Pt#2 and Pt#3 are settled in just 50 posts...try garnering some support against Pt#1, we can run this thread for another 25 posts or so before even Pt#1 is settled. My stand on Pt#1 is unmoved.

Your stand and your continuing game is not important in the greater scheme of things.
The accepted model and Interpretations stand as is.
If you chose to carry on for another 25 posts, that's your choice.
jcc will be finished his ban shortly, so you may have some support there.
Best of luck.

 

[paddoboy]

So, that brings me back to Post # 446, just below that enticing still face, .

Your post 446 was answered and explained in post 449, 450, 459, 466, 470, 471, 472, 485, and particularly 486 and 449. Apologies to the others that have attempted to show you the light [no pun intended] as I have only listed my own relevant posts.

 

[RajeshTrivedi]

The accepted model and Interpretations stand as is.

No doubt !! Whatever I have stated in my post #446 is accepted model and Interpretation thereof, that stands. You only attempted some half cooked interpretation or linkage and sadly others joined you in the soup unwittingly.

Since you have given up on Pt#1 as well, so the thread may rest in peace.