Lenz's law gives the direction of the induced emf resulting from electromagnetic induction, thus:

The emf induced in an electric circuit always acts in such a direction that the current it drives around a closed circuit produces a magnetic field which opposes the change in magnetic flux which produces the emf.

Lenz's law is consistent with the principle of conservation of energy. The law is named after the Baltic German physicist Heinrich Lenz, who formulated it in 1834.

See Maxwell's equations for further mathematical treatment.