30.5: Induced Electric Fields
The fact that emfs are induced in circuits implies that work is being done on the conduction electrons in the wires. What can possibly be the source of this work? We know that it’s neither a battery nor a magnetic field, as a battery does not have to be present in a circuit where current is induced, and magnetic fields never do any work on moving charges. The source of the work is in fact an electric field that is induced in the wires. For example, if a stationary conductor is placed in a changing magnetic field, an induced current starts flowing in the conductor. The source of this induced current is an electric field that is produced due to a change in magnetic flux. This field is called the induced electric field.
The work done by an induced electric field in moving a unit charge completely around a circuit is the induced emf, ε; that is,
where ∮ represents the line integral around the circuit. Faraday’s law can be written in terms of the induced electric field as
Thus, both the changing magnetic flux and the induced electric field are related to the induced emf from Faraday’s law.