Chapter 5 · Section 5.3
5.3 Faraday's Law of Induction
A magnetic flux that changes through a circuit, because the field varies or because the circuit moves, induces an electromotive force equal to minus its rate of change: Faraday's law of induction, the principle of every generator, transformer and motor, with Lenz's law fixing the sign.
- Faraday's law of induction in differential and in integral form, and the electromotive force of a circuit,
- the meaning of the minus sign (Lenz's law) and why it expresses the conservation of energy,
- the two ways to change a flux, the transformer emf of a fixed circuit in a changing field and the motional emf of a circuit moving through a field, and
- how to compute an induced emf step by step, and why the induced electric field has no potential.
The first Maxwell equation, , was discovered by Michael Faraday (1791–1867) in 1831, in a series of experiments in which he moved magnets near coils, switched currents on and off in neighbouring coils, and spun a copper disc between the poles of a magnet. In every case a current flowed in a closed conductor whenever the magnetic flux through it changed. The differential equation is the local statement. For circuits we need the integral form.
Contents of Section 5.3
Start reading →- 5.3.1The integral form
- 5.3.2The electromotive force
- 5.3.3The minus sign is Lenz's law
- 5.3.4The two ways to change the flux
- 5.3.5Recap
- 5.3.6Problems and solutions