Impedance
# Impedance

Impedance is the complex-valued generalization of resistance. It may refer to:

* Acoustic impedance, a constant related to the propagation of sound waves in an acoustic medium
* Electrical impedance, the ratio of the voltage phasor to the electric current phasor, a measure of the opposition to time-varying electric current in an electric circuit
   * High impedance, when only a small amount of current is allowed through
   * Characteristic impedance of a transmission line
   * Impedance (accelerator physics), a characterization of the self interaction of a charged particle beam
   * Nominal impedance, approximate designed impedance
   * Impedance matching, the adjustment of input impedance and output impedance
* Mechanical impedance, a measure of opposition to motion of a structure subjected to a force
* Wave impedance, a constant related to electromagnetic wave propagation in a medium
   * Impedance of free space, a universal constant and the simplest case of a wave impedance
