**Mutual inductance.** When a changing current in one circuit causes a changing magnetic flux in a second circuit, an emf is induced in the second circuit. and , – mutual inductance, – number of turns of coil of the first circuit, – average magnetic flux through each turn of coil 1.

**Self-inductance.** A changing current in any circuit causes a self-induced emf , – depends on the geometry of the circuit and the material surrounding it.

**Magnetic field energy.** An inductor with inductance carrying current has energy associated with the inductor’s magnetic field: . Magnetic energy density: .

**R-L**** circuits.** In an R-L circuit the growth and decay of current are exponential with time constant .

**L-C**** circuits.** An L-C circuit undergoes electrical oscillations with an angular frequency .

**L-R-C**** circuits.** The frequency of damped oscillations .