All electric circuits, a-c or d-c, include some combination of only three basic elements -- resistance, inductance, and capacitance. How much resistance is determined chiefly by an inherent material property people call resistivity. If resistivity is relatively low, as in many common metals, the material is considered a conductor. At constant voltage, higher resistance will decrease the current -- thus tending to drive conductor temperature back down. Long-term stability and insensitivity to temperature variations are desirable in electronic circuit design. That has led to development of thin-film resistors, in which the resistive element is not a higher-resistivity material such as carbon, but a metallic alloy -- normally a much better conductor. Close control of resistance in circuit components themselves is thus an obvious concern of all circuit designers. Resistance then, although probably the simplest basic property of any electrical circuit, can take some complex forms. They need to be fully understood by anyone involved in circuit design or system operation.
Circuit resistance: A not-so-simple property Richard L Nailen Electrical Apparatus; Nov 2008; 61, 11; Docstoc pg. 21
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