A magnetic field can create a current in a loop of wire, but only if the amount of field through the loop is changing.

• This is called an induced current.

• The process is called electromagnetic induction.

《 LOOKING BACK Chapter 29 Magnetic fields

A key idea will be the amount of magnetic field passing through a loop or coil. This is called magnetic flux. Magnetic flux depends on the strength of the magnetic field, the area of the loop, and the angle between them.

《 LOOKING BACK Section 24.3 Electric flux

Lenz’s law says that a current is induced in a closed loop if and only if the magnetic flux through the loop is changing. Simply having a flux does nothing; the flux has to change. You’ll learn how to use Lenz’s law to determine the direction of an induced current around a loop.

Faraday’s law is the most important law connecting electric and magnetic fields, laying the groundwork for electromagnetic waves. Just as a battery has an emf that drives current, a loop of wire has an induced emf determined by the rate of change of magnetic flux through the loop.

《 LOOKING BACK Section 26.4 Sources of potential

At its most fundamental level, Faraday’s law tells us that a changing magnetic field creates an induced electric field. This is an entirely new way to create an electric field, independent of charges. It is the induced electric field that drives the induced current around a conducting loop.

Electromagnetic induction is one of the most important applications of electricity and magnetism. Generators use electromagnetic induction to turn the mechanical energy of a spinning turbine into electric energy. Inductors are important circuit elements that rely on electromagnetic induction. All forms of telecommunication are based on electromagnetic induction. And, not least, electromagnetic induction is the basis for light and other electromagnetic waves.