I read many different explanation but none of them is satisfying. There is two cases:

  1. I move an iron rod in a magnetic field, between two bar magnet for example.

To this case I read that when I move the rod the electrons on it also move and moving charges produce magnetic field which interact with the external B field. I think this is impossible because those electrons don't move locally just relatively. This cannot produce net magnetic field arround the rod just allign the spin of the electrons. Maybe this B field interact with the external one?

  1. Iron core of a trafo transfer the energy.

In this case electrons in the secondary winding don't move at all. Allign to the external B field but just due to its spin magnetic moment. Just the spin allign and e- doesn't move at all. What causes the charge separation?


2 Answers 2


What causes the EMF?

  1. For a stationary conductor the EMF is caused entirely by electric fields. What happens is there are always electric fields when magnetic fields change. The induced electric fields and the changing magnetic fields have a common cause.

  2. For a moving conductor in an unchanging magnetic field, the EMF is caused by the magnetic field exerting a force on moving charges.

  3. For a moving conductor in a changing magnetic field, the EMF is caused by both electric and magnetic forces.

For your examples you need to look at whether things are moving and whether fields are changing. And whatever causes those things are ultimately responsible.

  • $\begingroup$ Waiting when you would answer. +1. $\endgroup$
    – user36790
    Commented Feb 15, 2016 at 15:46

If the magnetic flux change variably then induced current is produced which mean an induced emf is produced If the magnetic flux change uniformly then no current will be produced which mean that will be no induced emf. Engr Alamzeb Mehsud


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