Let us suppose we have a loop of wire with some definite resistance in a magnetic field. Let the magnetic field be varying. This varying magnetic field will st up an EMF in the wire. My questions are as follows:

1). Energy is dissipated across the wire resistance. Where does this energy come from?

2). The current generated in the loop will also generate a varying magnetic field. Will this magnetic field induce another EMF in the loop setting up another varying magnetic field? Will this go on indefinitely?


1 Answer 1


1) The energy comes form the aperture that creates varying magnetic field.

2) The process you describe (Lenz law) is fast convergent, since the induced magnetic field is much much smaller than the outer magnetic field. The process is instantaneous, so current within loop and total (outer and induced) magnetic field are immediately in the equilibrium.

  • $\begingroup$ How does this varying field get transformed to the an EMF? Could you please elaborate on the processes that occur at the molecular level during EMF induction? Another question i want to ask is about equilibrium you have mentioned. What exactly do you imply by an equilibrium? An explanation with some equations would be nice. Thanx in advance. $\endgroup$
    – Sidhant
    Jun 6, 2012 at 15:00
  • $\begingroup$ EMF is result of Maxwell's equations and there is no simple intuitive explanation on microscopic level. This is in particular connected to en.wikipedia.org/wiki/Faraday%27s_law_of_induction. As equlibrium is concerned, as you've pointed out in OP, outer magnetic field induces current that induces another magnetic field that induces another current... I just wanted to point out that this all happens instantaneously, so immediately you have total magnetic field and appropriate current. $\endgroup$
    – Pygmalion
    Jun 6, 2012 at 15:17

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