Homework Help: Electromagnetic induction and alternating currents

1. Feb 15, 2010

kihr

1. The problem statement, all variables and given/known data
A solenoid with an iron core inside it is connected in series with a resistance to a battery. What happens to the defelction in the ammeter connected in the circuit when the iron core is suddenly removed?

2. Relevant equations
Inductive reactance = wL
Induced e.m.f. = - dPhi/dt

3. The attempt at a solution

Alternative 1

We take w=0 since this is a d.c. circuit. Hence inductive reactance of the solenoid = 0. Therefore removing the iron core from the solenoid has no effect on the current.

Alternative 2

When the iron core is suddenly withdrawn from inside the solenoid, an e.m.f. is induced in the solenoid to oppose the change (i.e. reduction of the magnetic field inside it). Hence a momentary increase in current will take place as the solenoid will try to retain its initial magnetic field (B=Mu n I where Mu = permeability; n= no. of turns per unit length; I = current through solenoid).

In my opinion Alternative 2 is the correct answer. I would, however, like to receive comments / views of the Forum members. Thanks.