Say there are two concentric loops, and a variable magnetic field.

Due to the variable magnetic field, current is induced in both the loops, but is more in the case of the bigger loop.

So the bigger loop’s current (which is variable, since the magnetic field is variable) will try to induce current on the smaller loop too. This will lead to change in magnitude of the current.

But this isn’t so. The current is actually same for both loops. Why is my reasoning wrong?

  • $\begingroup$ Similar question : physics.stackexchange.com/questions/467051/… but I’m not satisfied with both the question and the answers. $\endgroup$
    – Natru
    Sep 27, 2021 at 15:13
  • $\begingroup$ I’m unclear on the setup here. Is the magnetic field uniform and external (i.e. generated by some other source entirely), or is it generated by an applied current through one of the loops (in which case, which one)? $\endgroup$
    – Gilbert
    Sep 27, 2021 at 15:29
  • $\begingroup$ Why do you think the current in ten larger loop is more? Or think of a coil why does not one loop of the coil influence the next one. $\endgroup$
    – trula
    Sep 27, 2021 at 15:35
  • $\begingroup$ @Gilbert magnetic field is produced by some other source entirely. $\endgroup$
    – Natru
    Sep 27, 2021 at 15:40
  • $\begingroup$ @trula Induced EMF is given as B.S, where B is the magnetic field and S is the area of the loop. More the area more will be the induced EMF and therefore more will be the current induced. $\endgroup$
    – Natru
    Sep 27, 2021 at 15:42

1 Answer 1


The bigger loop has bigger area for sure, but you are neglecting the fact that bigger loop means larger length resulting to higher resistance. Thus EMF induced is higher for bigger loop with higher resistance thus, same current is produced for both the wires.

  • $\begingroup$ Maybe it is the same. Or maybe not. The description of the problem omits critical details such as the resistances of the loops. $\endgroup$ Sep 27, 2021 at 20:58

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