Removing a charged coil from circuit
An inductor will actually stay charged for a time after you disconnect it.

You have built up a magnetic field around the inductor.  When you stop feeding it current, the magnetic field will change.  This should cause a current to flow, but the electric circuit is open leaving no path for the current.

The voltage rises, trying to keep the current flowing.  This goes on until the magnetic field is gone.

The voltage can get much higher than the voltage you used in the first place.

That is the basic core of boost converters.  They run a current through an inductor, then open the circuit.  The voltage goes up, and you can pick it off when it is high enough to suit your needs.



One of the worst electrical "zaps" I ever got was from a large inductor. 

I had a speaker that used a big coil and a piece of soft iron instead of a permanent magnet.

I switched off the power to the magnet coil, and touched a bare connection from it a little later.  

The voltage was pretty high.  Just a jolt, but it hurt like hell.