**NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW
VERSION:** "Mathematics of the Discrete
Fourier Transform (DFT), with Audio Applications --- Second
Edition", by Julius
O. Smith III, W3K
Publishing, 2007, ISBN 978-0-9745607-4-8. - Copyright ©
*2017-09-28* by Julius O. Smith III -
Center for Computer Research
in Music and Acoustics (CCRMA), Stanford University

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## Appendix B: Electrical Engineering 101

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 calledOhm’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

powerinwattsdissipated 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.