Impedance is the total opposition to current flow in an electrical circuit. It is made up of two components - Resistance and Reactance. It can be regarded as a way of extending Ohm's law to Alternating Currents.

In the context of the Blue Room, impedance is most commonly encountered when considering electrical properties of loudspeakers or cables.

Contents 1 Parallel and Series 2 Characteristic Impedance 3 Resistance 4 Reactance 5 See Also

Parallel and Series

Characteristic Impedance

A property of cables. more later.

Resistance

Opposition to DC current flow - the real part of the impedance, measured in Ohms. Resistance is lossy, i.e. power is lost as heat when current flows.

Reactance

Opposition to AC current flow - the imaginary part of the impedance, again measured in Ohms, but with a positive phase difference for inductors, and a negative phase difference for capacitors.

Remember C I V I L:

• Capacitors - I leads V.
• V leads I in L (L is commonly used as the symbol for inductance).

Pure reactance is lossless, i.e. no power is lost when current flows. It is however practically impossible to produce a pure reactance, there will always be a resistive (lossy) component.

See Also

• Power Factor
• Useful Equations

• Discussion