Re: inductor
Because of their magnetic field tends to be a conserbative field.
If you conect a volatge source in series with the inductor, that act like a pasive device, it takes the current and form a magnetic field that grows, that you can see as a opposition of a change in current.
The other case is when there a a source conected to the inductor and there are a magnetic field, and you cut the source, the energy in the magnetic field colapses and the inductor delivers, now act like a active device, energy in the form of current.
The law of faraday describe the behaviour of the inductor V = L di/dt