1. Michael Faraday discovered the principles of electromagnetic induction in the early 19th century through experiments showing that a changing magnetic field can induce an electromotive force (emf) in a nearby conductor. 2. Faraday's law of induction states that the magnitude of the induced emf is proportional to the rate of change of the magnetic flux through a circuit. 3. Generators and motors operate based on Faraday's law - a rotating coil of wire inside a magnetic field will experience a changing magnetic flux, inducing an emf to generate electricity in a generator, or experience a torque to cause rotation as a motor.