This is a purely hypothetical question as 0 resistance is impossible to create. That being said, I was thinking about this and came to a conclusion that I couldn't understand, so I assumed I must have gone wrong somewhere.

Motors turn thanks to interacting magnetic fields: an external field, and the induced magnetic field on a loop of wire. Time changing magnetic field induces a voltage. This voltage induces a current, determined by the resistance of the loop of wire. If this resistance in this wire is 0, like truly 0, like divide by 0 and get infinity 0, that means that the current through the wire would be infinite. This means the produced magnetic field would be infinite. This means that its interaction with the external field would be infinite, and could therefore provide infinite torques and forces in response to the external field no matter how small it is.

Now, given that we are bathed in EM waves all the time, what would this loop of wire do? I don't understand what would happen here.

The struggle is that I don't understand superconductors or advanced physics, beyond basic E&M.

  • $\begingroup$ As far as I know, superconductors really do have zero ohms of resistance. $\endgroup$
    – Tyberius
    Nov 16, 2017 at 19:59
  • 1
    $\begingroup$ @Tyberius like... literal 0 or just really really small? I had assumed just really really small. $\endgroup$ Nov 16, 2017 at 20:00
  • $\begingroup$ @Tyberius Ah, you are right! I didn't know this. A quick read showed me that the ejection of magnetic fields as superconductivity is achieved makes them NOT the magical impossible material I am referring to. (I think, this was a very quick read). $\endgroup$ Nov 16, 2017 at 20:02
  • $\begingroup$ They have zero resistance, but nonzero inductance. So the current cannot change infinitely fast. $\endgroup$
    – BowlOfRed
    Nov 16, 2017 at 20:04
  • $\begingroup$ @BowlOfRed ah... I think that is what I forgot to consider. The inductance of the coil itself will prevent an instantaneous response to the external field. ah, that's less exciting. Thanks tho. $\endgroup$ Nov 16, 2017 at 20:30

1 Answer 1


Time changing magnetic field induces a voltage.

Why? Let's stipulate that it is a loop of perfectly conducting wire (an idealization of course but instructive anyway).

Then, the time rate of change of magnetic flux threading the loop is zero and thus there is no induced emf to drive an 'infinite' current round the loop.

How can this be? Within the perfectly conducing loop circulates a current that changes at just the rate required to produce a changing magnetic flux threading the loop that precisely cancels the changing flux due to the external magnetic field.

In other words, as a comment points out, a perfectly conducting loop has an inescapable, non-zero self-inductance.


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