Appendix 3
Resistance, Impedance and Switching
A3.1 Electric Company Detective Sherlock Ohms
Electric current is the flow of electrically charged particles along a wire. (The particles that flow are usually electrons, which by convention have a negative charge as a consequence of Benjamin Franklin guessing wrong; therefore the direction of current flow is usually opposite the direction in which the particles actually move. Sorry.) A resistor is a device that doesn’t store electrical charges, but merely resists their flow. Electrical engineering starts with Ohm’s law: the voltage across a resistor is proportional to the current flowing through it. In mathematical terms:
(A3.1)
where I is the current, R the resistance, and V the voltage. Electrical ...
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