Do electrons radiate from electostatic acceleration?

[Lazarus]

Then at least tell me how a charge can change witout a current involved.

[swansont]

Then at least tell me how a charge can change witout a current involved.

Non sequitur. The equations don't require that the charge change. They require that the E field change.

[Lazarus]

Then how can the E field change without a current>

 

Also, how do Maxwlell's Laws knock an electron out of its cage 400 miles or 10 billion light years away?

[swansont]

Then how can the E field change without a current>

 

Also, how do Maxwlell's Laws knock an electron out of its cage 400 miles or 10 billion light years away?

You could, oh I don't know, accelerate a charged particle.

 

I have no idea what the second part is supposed to mean.

[Lazarus]

Swansont said:
You could, oh I don't know, accelerate a charged particle.

 

Reply:

I will settle for that. A magnetic field causes a electrostatic field that causes magnetic field.

 

Swansont said:
I have no idea what the second part is supposed to mean.

 

Reply:

That would be the photoelectric effect.

[swansont]

 

That would be the photoelectric effect.

 

Not covered by Maxwell's equations, which are classical.

[Lazarus]

I certainly appreciate all your comments.

[John Cuthber]

There was a proof?

In a sense

Proof by outrageous font size.

 

I haven't been following this thread but, as far as I can tell we know that accelerating electrons gives rise to em radiation in a number of cases.

The transmission of radio waves.

The production of X rays when fast electrons hit a target and - if you are looking for cases where a magnetic field does the acceleration, this

 

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

[decraig]

I haven't found a good answer to this. Deferring to charge accelerating in an antenna ignores all higher order terms.

 

The axial symmetric Larmor model seems to lead to energy conservation problems for a free particle. Maybe I'm mistaken.

 

What pattern of electromagnetic radiation results? The magnitude of the on-axis radiation is zero. Also, (1/2)(E^2+B^2) values are equal on each side of the yz-plane for charged particles traveling in the x direction, within a co-axial static electric field. This implies the kinetic energy of charges is not reduced by any radiation. This implies the static electric field is the source of radiated electromagnetic energy. But the electrostatic field remains unchanged after the particle has passed between the plates. This implies energy is not properly conserved.

Edited January 12, 2014 by decraig

[robinpike]

Swansont said:

The magnetic fields are much smaller, and deceleration is just a specific subset of acceleration. The electrostatic forces are responsible.

 

Reply.

A decrease in "speed" requires something to compensate for the lost kinetic energy. An increase in "speed" does not require a compensation.

 

As strict as you are about solid proof, it should be fair that there would be experimental evidence clearly influenced solely by electrostatic acceleration.

 

There was a previous topic that involved radiation from an accelerated electron.

 

The thing that puzzled me was what controlled how often the electron radiated a photon?

 

The explanations confused me a bit (from what I remember) and the answer involved how quick the acceleration occurred for the electron and that the path of the electron was near a nucleus.

 

However with an electrostatic field, the scenario seems to be simpler.

 

For example, if an electron is accelerated in a straight line (without hitting any atoms) down say a 10 foot vacuum tube, accelerated by an electrostatic field...

 

My question is how often does the electron radiate?

 

Is it from moment from moment? In which case, what defines the size of that 'moment'.

 

For example, does the electron radiate the lowest possible energy photon - and so a lot of them?

 

Or does the electron radiate just a few high energy photons?

 

I'm posting these questions again here, in case they are relevant to your questions Lazarus.

Edited March 30, 2015 by robinpike

[J.C.MacSwell]

Does an electron radiate while being accelerated by an electrostatic force or gravitational force?

 

 

From the original post...I skimmed through but did not see it covered and had not seen this thread prior to today (IIRC)

 

Does an electron in free fall radiate? (My thought would be no)

Does an electron forced to stay at rest in a gravitational field radiate? (It must...correct?? or am I off base?)

 

So I'm thinking electrons do not radiate due to gravitational forces (alone)

[swansont]

Linear acceleration will yield only a small amount of radiation, as the radiated power depends on the speed and acceleration. When the charge is accelerating a lot, it's not moving fast and when it's moving fast, it is not accelerating very much.

 

http://farside.ph.utexas.edu/teaching/em/lectures/node131.html (and preceding sections)

 

However, the source of the acceleration doesn't matter. We do magnetic accelerations because they are easier to construct for changing the path of a particle beam. But the divide between magnetic and electrostatic is artificial, as they are manifestations of the same force. The power emitted is the same in all frames (look at equation 1645 in the section previous to the one linked), and if you transform from the frame where the acceleration is purely magnetic into another arbitrary frame, some of the deflection (and thus radiation) will now be due to an electric field

[Enthalpy]

Does an electron in free fall radiate? (My thought would be no)

 

Do we have any theory to answer that question? My impression is "no".

 

Models of radiation by accelerated particles hold for a non-gravitational force and a Galilean acceleration. We have no solid theory that includes electromagnetism and gravitation.

 

Maybe some qualitative argument could tell, like an observer falling together with an electron - no idea.

 

Can experiments tell it? My impression is again "no", since the accelerations due to mass attraction are too small. Around an atom, a electron radiating light moves by 100pm at 1PHz, accelerating by 10²¹m/s² - and the radiated power depends steeply on the acceleration.

 

Maybe miniature black holes could accelerate electrons strongly enough, but we haven't seen any small black hole up to now.

 

Noise produced by the Van Allen belts, as they comprise many particles? The origin of the noise is essentially the magnetic twist of the trajectories, but could we distinguish a low-frequency component due to gravitation?

[imatfaal]

From the original post...I skimmed through but did not see it covered and had not seen this thread prior to today (IIRC)

 

Does an electron in free fall radiate? (My thought would be no)

Does an electron forced to stay at rest in a gravitational field radiate? (It must...correct?? or am I off base?)

 

So I'm thinking electrons do not radiate due to gravitational forces (alone)

 

It is funny how often this comes up. Please have a read of this thread

 

 

Falling Charges. Charge will radiate under gravitation/acceleration - and there is no potential problem with continual radiation in orbit (which would be kinda difficult to explain away)

 

https://www.scribd.com/doc/100745033/Dewitt-1964

Cecile Morette DeWitt and Bryce S. DeWitt. Falling charges. Physics, 1:3–20, 1964.

 

If you think about it if gravitational acceleration did not cause a charge to emit it would be a problem with equivalance

Funnily enough the same question popped up again a few pages later - with a better explanation from elfmotat

 

 

 

Yes. I remember going over this quickly when I first started studying GR. I've also looked up the question on a few other science boards and nearly everyone seems to agree with me. Plus, I just stumbled across this 1964 paper by DeWitt, which also agrees with me: https://www.scribd.com/doc/100745033/Dewitt-1964 . Of course we could all be missing something fundamental, but I doubt it.

 

The topic is apparently a lot more subtle than I originally thought!

 

 

 

Yes, I believe it should classically still radiate. It is different from the particle sitting on the ground because the particle on the ground has proper acceleration (i.e. a net force acting on it) due to the ground! Unless you mean the particle w.r.t. the Earth-Sun system as JonathanApps suggested. It should also classically radiate while it's stuck to the Earth orbiting the Sun.

 

 

 

Indeed. The observation of EM radiation is frame dependent, and accelerated observers co-moving with a charge will not detect any! But this isn't because it's not emitting any radiation, it's because the radiation lies beyond the Rindler horizon. See for example here: http://arxiv.org/pdf/physics/0506049‎ . (Of course this opens the philosophical question: if I can't measure it, is it really there? Which makes this a problem of definitions as well: what constitutes radiation? Does it need to be observable for all observers?)

 

 

To add to the previous comments about the testability of all this, Jackson does a calculation in section 14.2 for the energy per meter that would need to be supplied to an electron in a linear accelerator to get significant radiation loss, and it's ~10¹⁴ MeV/meter, which is far beyond what current linear accelerators are capable of (he gives the figure 50 MeV/meter).