27.2: Introduction


An electric circuit provides a complete path through which electrons may flow.  There are two basic types of circuits: series and parallel.  Devices in a series circuit are connected in one continuous loop while devices within a parallel circuit are connected in multiple loops.  A short circuit is a path of least resistance in the electrical circuit which bypasses the devices that the circuit is intended to operate.  When there is a short circuit, wiring may become hot.  Circuit diagrams show how the different types of circuits are connected together.  The lines in a circuit diagram represent wires.

The resistance is added differently in each type of circuit because of how current flows across each device in series versus parallel circuits.

Table $$\PageIndex{1}$$: Series and Parallel Resistance

Series Circuit Resistance

Parallel Circuit Resistance

$$R = R_1 + R_2 + R_3$$

$$\dfrac {1}{R} = \dfrac {1}{R_1} + \dfrac {1}{R_2} +\dfrac {1}{R_3}$$