Opposition that a circuit presents to electric current. It includes both resistance and reactance. Resistance arises from collisions of the current-carrying charged particles with the internal structure of the conductor. Reactance is an additional opposition to the movement of electric charge that arises from the changing electric and magnetic fields in circuits carrying alternating current. Impedance in circuits carrying steady direct currents is simply resistance. The magnitude of the impedance math.Z of a circuit is equal to the maximum value of the potential difference, or voltage math.V, across the circuit, divided by the maximum value of the current math.I through the circuit, or simply math.Z = math.V/math.I. The unit of impedance is the ohm.
Learn more about electrical impedance with a free trial on Britannica.com.
Z = the square root of (restoring force) times (inertia)
while the velocity of the wave is
v = the square root of (restoring force) divided by (inertia)
For example, for a sound wave the restoring force is the modulus of elasticity, while the inertia is just the density. For some waves (light waves, for example) it is not obvious how this simple picture for mechanical waves can be applied, but the same general picture holds.
Impedance may refer to: