Superconductors and induced current
A very short summary of super-conductors: they are conductors that provides no resistance to a current flowing through them. Despite the rather simplified explanation, they are an extremely complex study in quantum mechanics and a whole slew of scientific research besides. But for our purposes, the above definition shall suffice.
Now I'll introduce Ohm's law:
V=IR .... (1)V is voltage, I is current, R is resistance. So, given zero resistance in a super-conductor, one would logically expect therefore, to never measure a voltage across a superconductor, even if you injected an infinite amount of current. On a side note, superconductor have what is called a critical current above which they cease to be superconductors. And the last equation for the night, is one that gives the electric field (E) induced by a changing magnetic field, (B).
E = -dB/dt ... (2)Simply put, E is the negative gradient of B over time. Now here is what I am puzzling over:
- Let there be a changing B around a superconductor loop
- By (2) this would produce an electric field, and thus a voltage, in the superconductor loop
- Yet by (1) this is impossible, because anything multiplied by 0 gives 0
- I have made a mistake somewhere
- Ohm's law doesn't hold for superconductors.
- So what does happen when you try place a superconductor in a changing magnetic field?
- What would you measure?
Cheers, Steve
posted by steve @ 1:17 AM
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