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>>>>> "Hans" == Hans Aberg <haberg@xxxxxxxxxx> writes:
Hans> One has made an experiment, where a strong current was
Hans> induced in a superconductor, moving circularly then. It was
Hans> left for some years, and then the current was
Hans> measured. There was no measurable difference. One would
Hans> think the measurement itself somehow altered the current - I
Hans> do not know. But as far as one knows, the resistance in
Hans> superconductors is exactly 0, not a small positive number.
>> Paul was asking what happens when the current flowing through
>> the superconducting loop *changes*.
Hans> The electron pairs are accelerated, as they move in a loop.
>> Doesn't that involve emission/absorption of photons --
>> inevitably?
Hans> As far as I know, static magnets and superconductors do not
Hans> emit photons.
I'm talking about CHANGING currents. Not static ones.
Hans> The atoms have magnetic field, but only emit photons in
Hans> the connection with an electron changing orbit.
So, you believe an iron atom doesn't emit photons when you accelerate
the whole atom without exciting it's electrons? (Remember, the iron
atom is a small magnet. I'm thus talking about accelerating a
magnet!)
>> If you're going to keep a constant current on a
>> superconducting loop, how are you going to make use of it to do
>> computations?
Hans> That is for guy inventing the switch to figure out. :-) No
Hans> such switch exists - I just put in as an idea.
And I've been refuting this idea.
Making changes to EM fields must involve emission or absorption of
photons.
Hans> Some are claiming that this is wholly impossible. But that
Hans> was said about superconducting before superconductors was
Hans> discovered.
No. This has nothing to do with superconduction. Even in an
absolutely ZERO-resistance circuit, you would dissipate energy by
changing the current, because of the inevitable emission/absorption of
photons. That is the case even though you have ZERO resistance.
Simple calculations: suppose you have 2 charged capacitors C
maintaining different voltages V1 and V2. Now, you connect them
together, so that they can rebalance their charges to achieve the same
voltage across their ends. Suppose also that the circuit is
superconducting, so that no energy is dissipated as internal energy
during the charge-redistribution. Now, calculate the final,
equilibrium charges on the capacitors. Then, use the formula E = 0.5
C V^2 to compute the total energy stored in the capacitors before and
after the charge redistribution. Do you notice some energy loss?
Where to?
--
Lee Sau Dan 李守敦 ~{@nJX6X~}
E-mail: danlee@xxxxxxxxxxxxxxxxxxxxxxxxxx
Home page: http://www.informatik.uni-freiburg.de/~danlee
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