How does circuit complete through ground(earth)?

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GoldDigger said:
The sole exception to the highlighted statement, which is not in conflict with Ohm's Law, is the superconductor. You can have a current with no voltage drop as the resistance of the superconductor is really zero.
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Or take a lossless inductor. Apply an ac voltage. The emf induced in it is equal and opposite to applied voltage at any instant and so the resultant voltage in the circuit is always zero at any instant but the current is not zero!
 
Sahib said:
Or take a lossless inductor. Apply an ac voltage. The emf induced in it is equal and opposite to applied voltage at any instant and so the resultant voltage in the circuit is always zero at any instant but the current is not zero!
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Would you stick your wet fingers on it?
 
Smart $ said:
We are not talking abnormal [here-on-Earth] conditions.

Curious though... with no potential difference, which way does the current flow in this superconductor?
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Whichever way the magnetic field says! So long as the amount of current is changing, there will be a potential difference due to the impedance caused by the superconductor's inductance. Ohm's law still applies to that inductive impedance. The potential difference is only zero when the current is steady, but you can still tell which way it's flowing by the magnetic field it produces.
 
It is sort of a chicken versus egg situation.
If a superconducting coil is immersed in a time varying magnetic field, there cannot be a net voltage difference when you integrate the electric field around the closed loop. That means that the current in the superconducting loop will increase instantly in a way that completely balances the magnetic flux through the loop due to the external field.
The direction of current flow will be such as to cancel that field. No ambiguity at all.
 
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