A thought experiment -

Consider a very big loop of metal wire with the radius being 500 million km. Now, I have a powerful magnet stationary near the loop like this -

magnet and loop

Now, if I move the magnet emf must be generated in the loop according to Faraday's law. As the loop is very big, it will take some time for the deformation in electric and magnetic fields to reach the loop. So, when the information of the change in magnetic field is reaching the loop, won't there any emf be induced in the loop?

So, is the emf induced instantaneously or it will take some time for the current to flow?

  • $\begingroup$ If your loop is 500 Gm across, your magnet can only conceivably be "near" one part of it at a time. $\endgroup$
    – The Photon
    Commented Jun 22, 2017 at 16:11
  • $\begingroup$ @thephoton I don't understand what you mean to say. $\endgroup$ Commented Jun 24, 2017 at 5:54

1 Answer 1


It will take some time for the deformation of the magnetic field to reach the wire. The current will be induced when it does.

The induced current will generate a magnetic field. It will take some time for the induced field to reach the magnet. When it does, it will exert a force on the magnet.


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