Resistance, Electrical
Resistance, Electrical, the opposition that a material offers to the passage of an electric current. Resistance converts part of the electrical energy of the current into heat. The property of resistance has important applications in electrical and electronic devices.
Resistance is measured in units called ohms. A conductor has a resistance of one ohm when a voltage of one volt across it causes a current of one ampere. Stated as a formula, the relation between resistance, voltage, and current is
R=E/I
where R is the resistance in ohms, E the voltage in volts, and I the current in amperes.
In general, the resistance of a metallic conductor at a given temperature is constant. Thus the current through the conductor changes in proportion to the voltage. This relation is called Ohm's Law. The resistance of diodes, transistors, and other semiconductor devices usually depends in part on the voltage or current applied to them. Some substances lose all electrical resistance when they are cooled to very low temperatures.