Question

Imagine that you have a closed loop of wire sitting on a table and a bar magnet in your hand. You are allowed to move the magnet any way you’d like, but you may not touch the wire. Is there a way for you to produce a current in the wire? If so, how can you do it? If not, why not?

Imagine you have two wire loops lying next to each other on a table. The first one is connected to an AC power supply (like a wall outlet), producing a time-varying current through the wire, which in turn produces a time-varying magnetic field. The second wire loop reacts to this time varying magnetic field according to Faraday's law. Describe the current produced in the second loop.

Imagine you have two wire loops lying next to each other on a table. The first one is connected to a DC power supply (like a battery), producing a constant current through the wire, which in turn produces a magnetic field. The second wire loop reacts to this magnetic field according to Faraday's law. Does the second wire loop have any current flowing through it? Why/how is this situation different than with the AC power supply in the previous question?  

Answer 1

1) Yes, we can move the magnet away and near to the coil (loop) which will cause a change in magnetic flux through the loop and to oppose this, an induced current will be set up in the coil in a way such that it opposes field caused by moving magnet

2)  A time varying magnetic field induces a voltage that is proportional to the rate of change of the current producing it with a positive value indicating an increase in voltage and a negative value indicating decrease in voltage.

3) With a DC source, we will probably see a pulse of voltage on the second loop when the source is connected; the voltage will quickly fall to zero and will stay there until battery is disconnected, at which time an equal pulse of opposite polarity appears. With an AC source, we will see an AC voltage on the second loop as described above