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In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. [1]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. [2]
The DC wire resistance is an important parameter in transformer and general inductor design because it contributes to the impedance of the component, and current flowing through that resistance is dissipated as waste heat, and energy is lost from the circuit. It can be modeled as a resistor in series with the inductor, often leading to the DC ...
When the power source delivers current, the measured voltage output is lower than the no-load voltage; the difference is the voltage drop (the product of current and resistance) caused by the internal resistance. The concept of internal resistance applies to all kinds of electrical sources and is useful for analyzing many types of circuits.
There are, however, components of electrical circuits which do not obey Ohm's law; that is, their relationship between current and voltage (their I–V curve) is nonlinear (or non-ohmic). An example is the p–n junction diode (curve at right). As seen in the figure, the current does not increase linearly with applied voltage for a diode.
The lower the parallel resistance is, the more effect it will have in damping the circuit and thus result in lower Q. This is useful in filter design to determine the bandwidth. In a parallel LC circuit where the main loss is the resistance of the inductor, R, in series with the inductance, L, Q is as in the series circuit
For a circuit to be modelled with an ideal source, output impedance, and input impedance; the circuit's input reactance can be sized to be the negative of the output reactance at the source. In this scenario, the reactive component of the input impedance cancels the reactive component of the output impedance at the source.
Series circuits for train lighting were superseded, first by motor-generators, then by solid state devices. Series resistance can also be applied to the arrangement of blood vessels within a given organ. Each organ is supplied by a large artery, smaller arteries, arterioles, capillaries, and veins arranged in series.
The star-to-delta and series-resistor transformations are special cases of the general resistor network node elimination algorithm. Any node connected by N resistors (R 1 … R N) to nodes 1 … N can be replaced by () resistors interconnecting the remaining N nodes. The resistance between any two nodes x, y is given by: