Which law describes the magnetic field in a nonlinear wire?

Lenz's law

Explanation:

Lenz's Law states that the induced tensions will be such that they oppose the variation of the magnetic flux that produced them; However, this law is a consequence of the principle of conservation of energy.

Lenz's Law: "The sense of the currents or induced electromotive force is such that it always opposes the cause that produces it, that is, the variation of the flow."

Thanks to the already named Lenz Law, the Faraday Law was completed, so it is common to also call it the Faraday-Lenz Law to honor its efforts in the problem, Russian physicists always use the name "Faraday-Lenz Law ".