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Re: [Phys-L] closed loop superconductor circuit with current in vaccum



Another ‘Practical Application' is producing a volume of (near?) zero magnetic field by expanding a collapsed superconductor lead ‘balloon’.


On Oct 10, 2016, at 8:46 PM, John Denker <jsd@av8n.com> wrote:

On 10/10/2016 04:12 PM, Diego Saravia asked:

the only magnetic field is the produced by the current.

Is there any simple way to study what happens when you change the area of
that loop?

The flux trapped by a conducting loop is constant.

The result does not even require a superconductor, strictly speaking;
a classical "perfect" conductor suffices. A "pretty good" conductor
suffices, if the area is changed quickly enough.

This is an extreme example of Lenz's Law, which is itself a direct
corollary of the Maxwell equation:
Voltage = flux dot
If the voltage around the loop is zero, the flux is constant.
Nice and simple.

This has practical applications. You can produce a very large
magnetic field by setting up a current loop and then crushing
it suddenly (using e.g. explosives).

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