Series & Parallel Circuit Basics


  • Describe series and parallel circuits
  • Explain how series and parallel circuits are different
  • Demonstrate troubleshooting techniques based on Kirchhoff's voltage law

Series Circuits

In a series circuit, all voltage sources and loads are connected, end to end, to form a single path.

If any component of a series circuit becomes open or burnt out, current will be unable to flow.

This circuit shows 2 lamps in series connected to a battery. Because there is only one path, the current is the same through each lamp. But if Lamp 1 burns out, there will be no more current flow and therefore Lamp 2 will go out as well.

Lamp 1
Lamp 2

You may have experienced this type of connection with a string of lights.

If one of the bulbs burns out, all of the bulbs will go out.

Here's a typical series circuit operating a lamp. If the fuse blows or the switch is opened, the lamp will go out.


In a series circuit, because each load is connected one after the other, we determine the total resistance by adding all the loads together.

100Ω + 25Ω + 120Ω + 80Ω = 325Ω

By using Ohm's Law we can take the total resistance and the source voltage to calculate what the circuit current is.

12V / 325Ω = 0.037A = 37mA

A consequence of this is that if the amount of resistance is increased the current in the circuit will decrease.

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