Ziggurat
Penultimate Amazing
- Joined
- Jun 19, 2003
- Messages
- 64,377
Johan, before I get to a detailed response to your lost post to me, I want to go back again to something you said earlier, which is at the heart of what I'm going to object to in your more recent post.
If it stops and then jumps in another direction, that's an acceleration. If it stops at all, that's an acceleration. I'm at a complete loss as to why you think something can change its velocity without accelerating. That's the definition of acceleration. This is SUCH a fundamental error that until it's corrected, I don't think progress on other issues is really possible.
But regardless, here's my response to your most recent post.
As has been pointed out to you repeatedly, the cause of the acceleration is irrelevant. The linearity of Maxwell's equations should make this obvious.
They do accelerate, because everything moving in a circle MUST accelerate.
I'm not talking about generating the current, I'm talking about keeping the current moving in a circle. You cannot move in a circle without accelerating. This should be obvious. Why is it not?
And the fact that they do not emit radiation proves that you're wrong about acceleration always causing radiation.
First, you're wrong about what Onnes proved. He didn't prove that. That is, in fact, not provable at all. As has already been pointed out to you, NO measurement can ever establish that a voltage is identically zero, only that it's bounded by some upper nonzero value. If that bound is sufficiently small, we may assume that it's zero, but we sure as hell haven't proven it.
Secondly, in the example of a superconducting ring with a persistent current, the electric field causing acceleration is purely radial, so any voltage that creates is NOT along the direction of current flow.
And third, people apply nonzero voltages to superconductors all the time. That's how you get a current to flow in a superconducting magnet in the first place. This too has already been pointed out to you. A nonzero externally applied voltage typically results in a changing current, but even with zero resistance, a superconductor will still have impedence.
When you move in a circle at constant speed, you still experience constant acceleration. a = v2/r. Are you seriously unfamiliar with that equation? And there IS no work in that scenario, because the force is perpendicular to the displacement. No work, no change in energy, no radiation. But it's circular motion, so there MUST be an acceleration.
Then nothing is actually a superconductor. Because in every material which we call a superconductor, charge carriers can and do accelerate. If they didn't, they wouldn't be able to conduct at all.
No, that is not an experimental fact. It's a fact that under many conditions they will, but not in all conditions. Furthermore, it's also a fact that the cause of the acceleration is irrelevant, only the acceleration itself matters.
It can also first stop and then jump into another direction: there is then no acceleration involved.No no no---accelerating "along" a ring? No, we were specifically talking about how charge-carriers can negotiate a curve, a particular type of motion that involves acceleration. When a charge carrier moving at velocity {vx,vy} = {1,0} um/s turns left and ends up moving at {0,1} um/s, that is an acceleration. That is what we are talking about.
If it stops and then jumps in another direction, that's an acceleration. If it stops at all, that's an acceleration. I'm at a complete loss as to why you think something can change its velocity without accelerating. That's the definition of acceleration. This is SUCH a fundamental error that until it's corrected, I don't think progress on other issues is really possible.
But regardless, here's my response to your most recent post.
Not under the action of an electric-field.
As has been pointed out to you repeatedly, the cause of the acceleration is irrelevant. The linearity of Maxwell's equations should make this obvious.
If they did accelerate they would have emitted EM radiation.
They do accelerate, because everything moving in a circle MUST accelerate.
The fact that they do not emit radiation, proves that they are not generating the current by acceleration.
I'm not talking about generating the current, I'm talking about keeping the current moving in a circle. You cannot move in a circle without accelerating. This should be obvious. Why is it not?
And the fact that they do not emit radiation proves that you're wrong about acceleration always causing radiation.
This is in complete support with Onnes's original measurement which proves that when a current moves from one point to another within a superconductor, there is zero-voltage difference
First, you're wrong about what Onnes proved. He didn't prove that. That is, in fact, not provable at all. As has already been pointed out to you, NO measurement can ever establish that a voltage is identically zero, only that it's bounded by some upper nonzero value. If that bound is sufficiently small, we may assume that it's zero, but we sure as hell haven't proven it.
Secondly, in the example of a superconducting ring with a persistent current, the electric field causing acceleration is purely radial, so any voltage that creates is NOT along the direction of current flow.
And third, people apply nonzero voltages to superconductors all the time. That's how you get a current to flow in a superconducting magnet in the first place. This too has already been pointed out to you. A nonzero externally applied voltage typically results in a changing current, but even with zero resistance, a superconductor will still have impedence.
Why would it violate energy conservation? They radiate since they are accelerated all the time. This work must be radiated away or else their speed will keep on increasing
When you move in a circle at constant speed, you still experience constant acceleration. a = v2/r. Are you seriously unfamiliar with that equation? And there IS no work in that scenario, because the force is perpendicular to the displacement. No work, no change in energy, no radiation. But it's circular motion, so there MUST be an acceleration.
If they can accelerate the material is not a superconductor.
Then nothing is actually a superconductor. Because in every material which we call a superconductor, charge carriers can and do accelerate. If they didn't, they wouldn't be able to conduct at all.
The experimental fact remains that when you accelerate charges by an electric-field they will emit EM radiation
No, that is not an experimental fact. It's a fact that under many conditions they will, but not in all conditions. Furthermore, it's also a fact that the cause of the acceleration is irrelevant, only the acceleration itself matters.