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Series and Parallel Circuits

There are two basic ways to connect more than two circuit components (or loads): series and parallel. A series circuit is two or more electrical components connected end to end. A parallel circuit is when components are connected like the rungs of a ladder. 

Example of a Series Circuit:

The path of electrons from the (-) side to the (+) side goes through all the light bulbs.

If one light bulb burns out, then it acts like a switch and turns off the whole circuit

In a series circuit (assuming all the loads are equivalent), the voltage is split (or shared) equally between the loads. Each load gets the same current (amps). If the battery was a 9 Volt battery then each light would be receiving (using) 3 Volts.

This works the same for any type of load. If there were 3 motors in this circuit then each motor would be receiving (using) 3 Volts.

Example of a Parallel Circuit:

Each light bulb has its own direct path to both the (-) and (+) sides of the circuit.

If any bulbs go out, the circuit is still intact and the other lights will continue to burn.

In a parallel circuit every load receives the same voltage. If the battery was 9 Volts then each light would be receiving 9 Volts.

However, the current would be split between each of the paths (or loads). This is significant because if (for instance) you had 3 motors that each ran on 9 Volts connected in this manner, you would need to make sure that the battery was capable of outputting enough current to run all three motors. If one motor is made to work harder than the others it may "siphon" off current needed by the other motors causing them to stall.

You can also connect batteries in series or parallel

When batteries are hooked up In series, the voltage is increased. For example, two - 6 Volt batteries connected in series produce 12 Volts.

When batteries are hooked up in parallel, the voltage remains the same, but the power (or available current) is increased. This means that the batteries would last longer. For example two - 6 Volt batteries connected in parallel would still produce 6 Volts. But the two batteries would be able to power a 6 Volt device twice as long as a single battery.

If you decide to connect batteries in parallel or series you need to make sure that the batteries are the same. Do not mix different voltages and sizes of batteries in a series or parallel circuit.