1.2 Resistors

A resistor is simply a piece of material which resists the flow of charge through it. When you apply a voltage v across a resistor the current that flows through it, i, is given by Ohm's law
i = v/R
where R is the resistance in Ohms.

Resistors dissipate electrical power in the form of heat. The power dissipated (in Watts) is given by

P = iv = v2/R
The value of a resistor can be determined by measurement or by the resistor's colored markings. The colored lines shown in the picture of the resistor indicate its value in Ohms and its tolerance.