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Series and Parallel Circuits

Differences between single loop and multiple loop circuits through which current can flow.

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Series and Parallel Circuits

Only a licensed professional electrician like this one is qualified to install or repair the electrical system inside a home. It’s a complicated system that consists of a maze of electric circuits.

One Loop or Two?

An electric circuit consists of at least one closed loop through which electric current can flow. Every circuit has a voltage source such as a battery and a conductor such as metal wire. A circuit may have other parts as well, such as lights and switches. In addition, a circuit may consist of one loop or two loops.

Series Circuit

A circuit that consists of one loop is called a series circuit. You can see a simple series circuit below. If a series circuit is interrupted at any point in its single loop, no current can flow through the circuit and no devices in the circuit will work. In the series circuit below, if one light bulb burns out, the other light bulb won’t work because it won’t receive any current. Series circuits are commonly used in flashlights. You can see an animation of a series circuit at this URL: http://regentsprep.org/regents/physics/phys03/bsercir/default.htm

Q: If one light bulb burns out in this series circuit, how can you tell which bulb it is?

A: It may not be obvious, because neither bulb will light if one is burned out. You can tell which one it is only by replacing first one bulb and then the other to see which replacement results in both bulbs lighting up.

Parallel Circuit

A circuit that has two or more loops is called a parallel circuit. A simple parallel circuit is sketched below. If one loop of a parallel circuit is interrupted, current can still flow through the other loop. In the parallel circuit below, if one light bulb burns out, the other light bulb will still work because current can bypass the burned-out bulb. The wiring in a house consists of parallel circuits. You can see an animation of a parallel circuit at this URL: http://www.regentsprep.org/regents/physics/phys03/bparcir/default.htm


Take the quiz at the following URL and then check your answers. http://www.twothirtyvolts.org.uk/education/revision-quiz/electric-circuits-11to14.html


  1. Compare and contrast series and parallel circuits.
  2. Sketch a series circuit that contains a voltage source and three light bulbs.
  3. Is it possible to place a switch in this circuit to control only one light?
  4. Sketch a parallel circuit that contains a voltage source and three light bulbs.
  5. Where should you place a switch to turn all the lights on and off?
  6. Where should you place a switch to turn only one light on and off?

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