Electric Circuits with Multiple Loads

10.7

Some electric devices, such as calculators, simple cameras, and flashlights, operate only one electric load at a time. However, when strings of lights or the lights in a car are turned on, several loads are operating simultaneously. There are two kinds of circuits used to connect multiple loads: the series circuit and the parallel circuit.

Series Circuits

A series circuit is when the parts in a circuit are connected so that there is only a single pathway for the current to flow through.

The three light bulbs are connected in a series circuit. When the switch is closed, all three bulbs produce light. When a bulb burns out, the current is unable to flow through the circuit, just as if a switch were open. When one bulb burns out the whole circuit stops working!

• When a second resistor is added in series to the first resistor, the total resistance is doubled. Also, the total current flowing through a circuit decreases as each resistor is added.

Parallel Circuits

• A parallel circuit is when the elements in a circuit are connected in such a way that there is more than one pathway for the current to flow through. Just because one bulb burns out doesn’t mean it affects the others.

• Each time another resistor is added in parallel to the circuit, the total resistance decreases. The total current from the battery is increased when the circuit is parallel. In any parallel circuit, the total current flowing from the source of electrical energy equals the sum of all the separate branches in the circuit.