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## Homework Statement

This problem arises from a much larger essay/lab/project thing. I know that there is an induced current in the wire of an AC electromagnet because the magnetic field is constantly changing along with the AC current, so it makes sense to me that will produce a constantly changing emf as well which could be effectively adding or subtracting voltage of the wire in the electromagnet, which in turn slightly changes the magnetic field of the electromagnet. The larger project concerns speakers, which use an electromagnet in conjunction with a permanent magnet to oscillate the driver/cone at the same frequency as the AC current with an amplitude determined by the changing voltage of the AC current. The amplitude thing makes the EMF important. That and the lower limit of the essay word count.

## Homework Equations

I didn't go quite this far into electromagnetism in my physics class, so figuring out what the relevant equations are is part of the process.

I=I

_{0}cos(2*pi*ft)

I=V/R

B=I*mu

_{0}/(2pi*r)

Not sure about the one directly above. Apparently it is just for a straight wire. If so I'd need something that relates the current in the wire to the magnetic field in the wire. I also have no idea how to incorporate the ferromagnetic core into the whole situation.

emf=-N*dPhi/dt

## The Attempt at a Solution

I=V

_{0}*cos(2*pi*f*t)/R

B=V

_{0}cos(2*pi*f*t)/(2*pi*r*R)

Phi=AV

_{0}cos(2*pi*f*t)/(2*pi*r*R)

emf=-NAV

_{0}cos(2*pi*f*t)/(2*pi*r*R*dt)

emf=NAV

_{0}f*sin(2*pi*f*t)/(r*R)

Didn't work. Also, this is the first time I've used legitimate mathematical calculus in a legitimate physics situation.

I still want to do something on my own, but it would be great if someone could fill the missing base pieces of "What formula should I use that relates I of a solenoid to the created B in a solenoid?" and "How do I incorporate the magnetic field of the core?"

Oh and let me know if I'm completely off in my concepts too, haha.