|“||The induced current is always directed such that it always acts contrary to its cause.||”|
It is necessary for there to be conservation of energy. It comes from the fact that the induced current produces a magnetic field in addition to the one that caused the induced current. Faraday's law describes induction mathematically relating the voltage induced, V, to the magnetic flux, ΦB , as:
The minus sign represents Lenz's law, that the induced voltage (and therefore current that might flow) will oppose the flux that is causing it.