impedance

(noun)

A measure of the opposition to the flow of an alternating current in a circuit; the aggregation of its resistance, inductive and capacitive reactance. Represented by the symbol Z.

Related Terms

Examples of impedance in the following topics:

  • Impedance

    • The phase of the complex impedance is the phase shift by which the current is ahead of the voltage.
    • This quantity is known as the element's (complex) impedance.
    • The impedance of a resistor is R, while that of a capacitor (C) is $\frac{1}{j \omega C}$.
    • In the case of the circuit in , to find the complex impedance of the RC circuit, we add the impedance of the two components, just as with two resistors in series: $Z = R + \frac{ 1}{j \omega C}$.
    • The (real value) impedance is the real part of the complex impedance Z.

  • RLC Series Circuit: At Large and Small Frequencies; Phasor Diagram

    • By combining Ohm's law (Irms=Vrms/Z; Irms and Vrms are rms current and voltage) and the expression for impedance Z, from:
    • If the frequency is high enough that XL is much larger than R as well, the impedance Z is dominated by the inductive term.
    • This response makes sense because, at high frequencies, Lenz's law suggests that the impedance due to the inductor will be large.
    • The impedance Z at small frequencies $(\nu \ll \frac{1}{\sqrt{2\pi LC}})$ is dominated by the capacitive term, assuming that the frequency is high enough so that XC is much larger than R.

  • Bursitis

    • Bursitis, the inflammation of bursae (small sacs) of synovial fluid, impedes the movement of muscles and tendons over joint bones.

  • Resonance in RLC Circuits

    • Combining Ohm's law, Irms=Vrms/Z, and the expression for impedance Z from
    • At some intermediate frequency $\nu_0$, the reactances will be equal and cancel, giving Z=R —this is a minimum value for impedance, and a maximum value for Irms results.

  • Gender and Diversity

    • Diversity, while an important part of a strong workforce, can contribute to misconceptions that may impede communication.

  • Phase Angle and Power Factor

    • As we studied in a previously Atom ("Impedance"), current, voltage and impedance in an RC circuit are related by an AC version of Ohm's law: $I = \frac{V}{Z}$, where I and V are peak current and peak voltage respectively, and Z is the impedance of the circuit.

  • The Limits of Progressivism

    • Although the Progressive Era was a period of social progress, it also had multiple, contradictory goals that impeded reform efforts.
    • Although the Progressive Era was a period of broad reform movements and social progress, it was also characterized by loose, multiple, and contradictory goals that impeded the efforts of reformers and often pitted political leaders against one another, most drastically in the Republican Party.

  • Resistance and Resistivity

    • Resistance and resistivity describe the extent to which an object or material impedes the flow of electric current.
    • Resistance is the electric property that impedes a current.

  • Burns

    • Migration of immune cells is hampered by destruction of the vasculature, and there is a release of inflammatory intermediaries that impede the immune response.

  • Koch's Postulates

    • Attempts to rigidly apply Koch's postulates to the diagnosis of viral diseases in the late 19th century, at a time when viruses could not be seen or isolated in culture, may have impeded the early development of the field of virology.