E & M

[Physicsisfun2005]

Problem:
A hundred turns of insulated copper wire are wrapped around an iron cylinder of cross-sectional area 1x10^-3 sqr. m and are connected to a resistor. The total resistance in the circuit is 10 ohms. If the longitudinal magnetic field in the iron changes from 1.0 T in one direction to 1.0 T in the opposite direction, how much charge flows through the circuit.

I was wonderin why the direction will affect the magnitude of the charge?

[Diane_]

I suspect they're talking about the total charge. The system as you describe it is not connected to a battery, so in steady-state there is no current in the circuit. If you change the magnetic field in the core, you're going to induce a voltage, with the corresponding current flow. This will continue until a new steady-state of no current is achieved. It looks to me like the question is asking how much charge will flow through the circuit between one state and the other.

[Physicsisfun2005]

Is a emf emitted?.......Faraday's Law or Lenz's Law I think but how do I apply it?....

[Diane_]

You have a conducting coil with a magnetic field passing through it, right? Any change in that field will induce a voltage in the coil, just as any change in the current through the coil will induce a magnetic field.

Methinks you need to run back over the section on electromagnetic induction in your text.

[eridanus]

Is a emf emitted?.......Faraday's Law or Lenz's Law I think but how do I apply it?....
faraday's law:
E = N\Delta\Phi/\Delta t
or induced voltage equals the number of loops times the change in flux over change in time
direction matters because flux is a vector. so the change in flux would be (1.0 T)(1x10^-3 sqr. m)-(-1.0 T)(1x10^-3 sqr. m)
change in flux is proportional to emf and emf to current

[Diane_]

faraday's law:
E = N\Delta\Phi/\Delta t
or induced voltage equals the number of loops times the change in flux over change in time
direction matters because flux is a vector. so the change in flux would be (1.0 T)(1x10^-3 sqr. m)-(-1.0 T)(1x10^-3 sqr. m)
change in flux is proportional to emf and emf to current

Not to get all Forum Police-y, but it is better to let him work it out on his own. Yes, I have problems doing that, too. :)

[Physicsisfun2005]

thanx ;).......i figured i'd use that equation.