Voltage, Current, and Resistance

The state of an ideal resistor is completely specified by the voltage across it (call it volts) and the current passing through it ( amperes, or simply ``amps''). The ratio of voltage to current gives the value of the resistor ( resistance in Ohms). The fundamental relation between voltage and current in a resistor is called Ohm's Law:

where we have indicated also that the voltage and current may vary with time (while the resistor value normally does not).

The electrical power in watts dissipated by a resistor R is given by

where is the voltage and is the current. Thus, volts times amps gives watts. Also, volts squared over ohms equals watts, and so on.

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.