Another radiation question

  • Thread starter anonymous299792458
  • Start date
  • Tags
    Radiation
In summary: The connection between an accelerated charge an and one at rest in a (weak) gravitational field is discussed in accordance with the principle of equivalence principle. For that purpose, the fields produced by a freely falling charge and a supported one (i.e. at rest in a gravitational field) are transformed to the rest frame of the observer, who may be similarly supported or freely falling. A nonvanishing energy flux is found only if the charge is freely falling...
  • #1
anonymous299792458
9
0
If a charge is accelerating, but you are also accelerating WITH the charge, will you see any radiation? I.e. will the integral of the Poynting vector over a closed surface surrounding the charge be zero? It seems that it should be.

Now let's say YOU are accelerating, but the charge is NOT. You woudn't see radiation from the charge in this case, will you?
 
Science news on Phys.org
  • #2
for the first question, yes, you will see radiation
for the second question, No, you won't wee radiation

remember you are not in inertial reference fram in both case, you have no reason to expect the answer is same as you sitting in an inertial reference... velocity is relative, but accelerating is absolute, which is independent to the observer's motion... the charge feels acceleration. and an accelerating charge emits radiation, period

it is a bit weird in the first case because you do not see the charge moving and it radiates, but again, you are not in the inertial frame, same as you see stuffs behave weird when were in an accelerating bus...
 
  • #3
vincentchan said:
for the first question, yes, you will see radiation
for the second question, No, you won't wee radiation

remember you are not in inertial reference fram in both case, you have no reason to expect the answer is same as you sitting in an inertial reference... velocity is relative, but accelerating is absolute, which is independent to the observer's motion... the charge feels acceleration. and an accelerating charge emits radiation, period

it is a bit weird in the first case because you do not see the charge moving and it radiates, but again, you are not in the inertial frame, same as you see stuffs behave weird when were in an accelerating bus...
Yes, yes, that's what I would have thought too (and you may very well be right). But let's say we have a charge sitting on a table in the Earth's gravitational field. I don't think you'll measure any radiation, otherwise you'd have a source of "free" energy. Locally, this is equivalent to the charge being in an accelerating reference frame and you accelerating with the charge. So, I would assume that in the latter case the radiation you'd measure would also be zero.
 
  • #4
So, I would assume that in the latter case the radiation you'd measure would also be zero.
latter case? did u mean the former case?
if you have a charge on Earth and you are rotating with it... you WILL see radiation... just the rotation of the Earth is too slow (1 rotation / day) that the radiation is far too small for us to detect it...
and NO, you won't get free energy... the rotation of Earth will slow down by the charge when it radiate, you have a price to pay... the day is longer (by a tiny amount). again, the effect will be too small for us to detect...
 
  • #5
vincentchan said:
latter case? did u mean the former case?
if you have a charge on Earth and you are rotating with it... you WILL see radiation... just the rotation of the Earth is too slow (1 rotation / day) that the radiation is far too small for us to detect it...
and NO, you won't get free energy... the rotation of Earth will slow down by the charge when it radiate, you have a price to pay... the day is longer (by a tiny amount). again, the effect will be too small for us to detect...
I wasn't talking about rotation. I was talking about the equivalence principle which states that a gravitational field is locally equivalent to an accelerating reference frame.
 
  • #6
anonymous299792458 said:
If a charge is accelerating, but you are also accelerating WITH the charge, will you see any radiation?
No.
I.e. will the integral of the Poynting vector over a closed surface surrounding the charge be zero? It seems that it should be.
The Poyting vector will be zero.
Now let's say YOU are accelerating, but the charge is NOT. You woudn't see radiation from the charge in this case, will you?
You will "see" radiation in your frame.

Pete
 
  • #7
Um, we've got two completely opposite answers here from pmb phy and vincenchan...
 
  • #8
anonymous299792458 said:
Um, we've got two completely opposite answers here from pmb phy and vincenchan...
I'm going by results established in the physics journals. E.g. see -
http://www.geocities.com/physics_world/misc/falling_charge.htm

For example Radiation from an Accelerated Charge and the Principle of Equivalence, A. Kovetz and G.E. Tauber, Am. J. Phys., Vol. 37(4), April 1969
Abstract: The connection between an accelerated charge an and one at rest in a (weak) gravitational field is discussed in accordance with the principle of equivalence principle. For that purpose, the fields produced by a freely falling charge and a supported one (i.e. at rest in a gravitational field) are transformed to the rest frame of the observer, who may be similarly supported or freely falling. A nonvanishing energy flux is found only if the charge is freely falling and the observer supported, or vice versa. This agrees with previously established results.

Pete
 
  • #9
pmb_phy said:
Radiation from an Accelerated Charge and the Principle of Equivalence, A. Kovetz and G.E. Tauber, Am. J. Phys., Vol. 37(4), April 1969
This article is now online at

http://www.geocities.com/physics_world/misc/falling_charge.htm

Scroll down to the article and click the title. The title links to a PDF file containing the article.

Pete
 
  • #10
pmb_phy:
your article seems confirms what i said... and it explain very clearly ...
did your conclustion based on that article? or it is your own thought... If it is your own thought, why bring up something contradict your argument :rolleyes:
 
  • #11
vincentchan said:
pmb_phy:
your article seems confirms what i said... and it explain very clearly ...
did your conclustion based on that article? or it is your own thought... If it is your own thought, why bring up something contradict your argument :rolleyes:
Please clarify. The question was
If a charge is accelerating, but you are also accelerating WITH the charge, will you see any radiation?
I responded "No." As the article states in the abstract
A nonvanishing energy flux is found only if the charge is freely falling and the observer supported or vise versa.
Please explain how my answer is in contradiction with that?

Pete
 
  • #12
A nonvanishing energy flux is found only if the charge is freely falling and the observer supported or vise versa.

Please explain how my answer is in contradiction with that?

here is one of the newest research done by last year...
http://arxiv.org/PS_cache/gr-qc/pdf/9303/9303025.pdf [Broken]
go to page 15 and read the conclusion...

edit: the 10th line..."in the accelerated frame..." don't want to quote every thing, read...
 
Last edited by a moderator:
  • #13
vincentchan said:
here is one of the newest research done by last year...
http://arxiv.org/PS_cache/gr-qc/pdf/9303/9303025.pdf [Broken]
go to page 15 and read the conclusion...

edit: the 10th line..."in the accelerated frame..." don't want to quote every thing, read...
You didn't explain how what I said contradicted the articles I quoted/referanced.

I've already read the article the you referred to. The author contradcits a lot of physics in that article. For example; the author assumes, using his own intuition or whatever, that some forms of the equivlance principle don't apply. Since the equivalence principle is a postulate then only experimentation can determine whether it is correct or not - not calculation.

The author asserts
Since the particle is radiating energy which can be detected and used, conservation of energy suggests that the radiated energy must be furnished by the rocket — we must burn more fuel to produce a given accelerating worldline than we would to produce the same worldline for a neutral particle of the same mass.
This contradicts previous conclusions. For example; An extra force must be used to accelerate a charged particle over a non-charged particle. This extra force is known in the literature as the "self-force" acting on the particle. This also is known as the "radiation reaction force."


Details - The power radiated by an accelerating charge is given (in esu units) by P = (2/3)q2/c[sup3[/sup](a)2. To account for this energy loss modify Newton's equation by adding in an extra force Frad. Suppose the force on a non-charged particle of the same (rest) mass is (in the non-relativistic limit) Fext = ma. A particle with charge q and mass m is then given by Fext + Frad = ma. By demanding that energy be conserved this demands Frad = mTda /dt (where T is a constant and I'm too lazy to type it in :tongue: ). If the particle is uniformly accelerated then the radiative force is zero. Thus if you have a particle in a uniformly accelerating frame of reference and you're also at rest in that frame then the weight of the particle is independant of the charge. Hence the authors assertions are in contradiction with the assertions I've just stated.

Its also be shown that the weight of a particle depends on the spacetime curvature. That means that a charged particle at rest on, say, the Earth will have a different weight (i.e. smaller required support force) than the same particle at rest in a uniform g-field.

The paper is newer. That doesn't mean that its better.

Pete
 
Last edited by a moderator:
  • #14
  • #15
I.e. will the integral of the Poynting vector over a closed surface surrounding the charge be zero? It seems that it should be.
pmb_phy said:
The Poyting vector will be zero.

The article Vinchentan cited says:
Although each observer in a rigidly accelerating elevator surrounding the particle measures a vanishing Poynting vector in his own private rest frame, nevertheless, taken as a whole there is radiation through the elevator walls. Adding the (zero) energy fluxes measured by each observer on the wall in his private rest frame to (incorrectly) conclude zero total energy radiation is an illegitimate operation because these energy fluxes refer to different rest frames.

Is this/can this/how can this be true?
 
  • #16
da_willem said:
Well, not really. It goes to an article about the mass of a photon gas...
Sorry. I screwed up the names. I'll correct it later.
Is this/can this/how can this be true?
In my opinion the author Vinchentan cited is wrong.

Pete
 

1. What is radiation?

Radiation is a form of energy that is emitted in the form of waves or particles. It can come from natural sources, such as the sun and radioactive materials, or from man-made sources, such as X-rays and nuclear power plants.

2. What are the different types of radiation?

There are three main types of radiation: alpha, beta, and gamma. Alpha radiation consists of helium nuclei, beta radiation consists of electrons or positrons, and gamma radiation is a form of electromagnetic radiation.

3. How is radiation harmful to humans?

Radiation can damage living cells by breaking chemical bonds and causing mutations in DNA. This can lead to health effects such as cancer, genetic disorders, and radiation sickness.

4. How can we protect ourselves from radiation?

To protect ourselves from radiation, we can limit our exposure by using protective equipment, monitoring our surroundings for high levels of radiation, and following safety protocols in areas where radiation is present. We can also limit our exposure to man-made radiation sources, such as X-rays and nuclear power plants.

5. What are the benefits of radiation?

Radiation has many beneficial uses in various fields, such as medicine, energy, and agriculture. It is used in cancer treatments, imaging techniques, and sterilization processes. Radiation is also a source of energy production and can be used in food preservation and pest control in agriculture.

Similar threads

  • Thermodynamics
Replies
2
Views
1K
  • Thermodynamics
Replies
23
Views
18K
Replies
14
Views
1K
  • Thermodynamics
Replies
5
Views
678
Replies
7
Views
1K
  • Special and General Relativity
Replies
13
Views
1K
  • Thermodynamics
Replies
6
Views
1K
  • Thermodynamics
Replies
8
Views
1K
Replies
5
Views
1K
Back
Top