Here is a question I had.... Not sure how I should have went about answering.

A DC coil induces a AC alternator. Coil power 300 watts and circuit 12 amps. Alternator output 125v at 12 amps.

1) Find resistance in coil.
2) Find Impedance in coil.
3) Find power dissipated in AC circuit.

Any help greatly appreciated.

 

1. If you are given the power dissipated in the coil winding (resistance) and the current you can find the resistance.

2. You are not given any information about the coil inductance and since the coil is supplied by a DC source the value of the impedance cannot be determined.

3. The alternator output power is what is delivered to the AC circuit - 125V (RMS?) at 12A (RMS?) - provided you assume a unity power factor (what else can you do given the lack of detail) then the power in the AC circuit can be determined also.

 

Although I guess you can reasonably argue in the case of impedance (2.) that since

Z = Rcoil + jwLcoil

and since w=0 at DC, then coil impedance Zcoil = Rcoil