Dropping bar magnet through loop of wire

1. Aug 7, 2009

So I know that a current is induced when the magnetic field changes near the wire. So say I dropped the magnet North end up and South end down through this wire, the current would increase as it was nearing it, and decrease as it leaves it.

1) is this correct?
2) what happens in the short time period that the magnet is still passing through the coil? is the current 0?

2. Aug 7, 2009

Bob S

If your signal is going into a low impedance ammeter, the current would go positive (or negative depending on polarity of ammeter), go back to zero while the magnet is passing through the wire, then go negative (opposite polarity) as the other pole passes through the loop. It is a bipolar signal. The reason it goes to zero in the middle of the magnet is because dB/dt through the loop is zero.

If you built a voltage integrator with an operational amplifier, the integrated voltage would stay positive until the other end of the magnet passed through the loop.