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

A superconductor can't be in a magnetic field, remember? Eddy currents are induced on its surface such that the magnetic field in the superconductor is zero. As well as a critical current, supercondcutors also have a critical magnetic field above which they cease to superconduct.

ReplyDeleteM.

You'd want to look for bananas. :P

ReplyDelete