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Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.What follows below is a derivation of impedance for each of the three basic circuit elements: the resistor, the capacitor, and the inductor. The magnitude gives the change in voltage amplitude for a given current amplitude through the impedance, while the exponential factors give the phase relationship.ĭeriving the device-specific impedances The impedance of a two-terminal circuit element is represented as a complex quantity Z The impedance caused by these two effects is collectively referred to as reactance and forms the imaginary part of complex impedance whereas resistance forms the real part.Ī graphical representation of the complex impedance plane In addition to resistance as seen in DC circuits, impedance in AC circuits includes the effects of the induction of voltages in conductors by the magnetic fields ( inductance), and the electrostatic storage of charge induced by voltages between conductors ( capacitance). Arthur Kennelly was the first to represent impedance with complex numbers in 1893. The term impedance was coined by Oliver Heaviside in July 1886. 4.3 Deriving the device-specific impedances.Instruments used to measure the electrical impedance are called impedance analyzers. The reciprocal of impedance is admittance, whose SI unit is the siemens, formerly called mho. In multiple port networks, the two-terminal definition of impedance is inadequate, but the complex voltages at the ports and the currents flowing through them are still linearly related by the impedance matrix. The notion of impedance is useful for performing AC analysis of electrical networks, because it allows relating sinusoidal voltages and currents by a simple linear law. However, Cartesian complex number representation is often more powerful for circuit analysis purposes. Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the polar form | Z| ∠θ. Impedance is a complex number, with the same units as resistance, for which the SI unit is the ohm ( Ω). Impedance extends the concept of resistance to alternating current (AC) circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. In general, it depends upon the frequency of the sinusoidal voltage. Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit.
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