The law that gives the direction of an induced current is Lenz’s law. It states that an induced current flows in a direction that creates a magnetic field opposing the change in magnetic flux that produced it.
Lenz’s law is represented by the minus sign in Faraday’s law of electromagnetic induction: the induced electromotive force is proportional to the negative rate of change of magnetic flux. If magnetic flux through a loop increases, the induced current creates a field opposing that increase. If the flux decreases, the induced field supports the original direction to resist the decrease.
Heinrich Lenz formulated the law in 1834. It is a direct consequence of conservation of energy: if the induced current reinforced the change instead of opposing it, systems such as generators and electromagnetic brakes could produce energy without an input.
Faraday’s law determines the magnitude of the induced voltage as well as the overall induction relationship, but Lenz’s law specifically identifies its direction. Ohm’s law relates voltage, current, and resistance, while Ampère’s law connects currents with magnetic fields.