What principle explains how a changing magnetic field can produce electric current?

Faraday's law of induction is the principle that describes how a changing magnetic field can induce an electric current in a conductor. This phenomenon occurs because when the magnetic field around a conductor changes, it creates an electromotive force (EMF) within the conductor. The rate of change of the magnetic field is directly proportional to the induced EMF and consequently the electric current generated.

This principle is foundational in many electrical technologies, including generators and transformers, where the manipulation of magnetic fields is used to create usable electric power. Understanding this law is crucial for explaining various electromagnetic applications and devices used in modern technology. The other principles mentioned do not pertain to the relationship between magnetic fields and electric currents in the way Faraday's law does.