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THE PARALLEL CIRCUIT

After reading this section you will be able to do the following:

  • Define a parallel circuit and explain how it compares to a series circuit.
  • Construct a parallel circuit.
  • Explain what a voltmeter does and how it is different from an ammeter.

Like the series circuit, parallel circuits also contain a voltage (current) source as well as wires and other components. The main difference between a series circuit and a parallel circuit is in the way the components are connected. In a parallel circuit the electricity has several paths that it can travel.

Try building this simple parallel circuit

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Congratulations! You have just built a parallel circuit. Notice that when you closed the switch, the electrons flowed through both loads at the same time. In our series circuit, all the electrons flowed through all the components in order. With the parallel circuit, some electrons go through one load and some go through the other load, all at the same time. At point A, the total current splits up and takes different paths before the circuit joins back together again at point B.

A parallel circuit exists whenever two or more components are connected between the same two points. Those two points in this circuit are points A and B. Both resistors connect to both points A and B.

Each parallel path is called a branch of the parallel circuit.

Try building this parallel circuit, now including a voltmeter

This parallel circuit contains 3 branches (two resistors and a voltmeter), which means the electron current goes through all three branches at the same time. We put a voltmeter on this second circuit to show an important fact. In the last 4 circuits you made, you included an ammeter into them. Ammeters must always be placed in series in a circuit, otherwise they will not work. The voltmeter we added in the last circuit has a different requirement in order to work. Voltmeters must be placed in parallel with the circuit in order to work. This is because voltage meters measure the difference in electromotive force (EMF) from one area to another. They are used to measure the difference in EMF on one side of a component compared to the other side of the component. In our homes, most circuits contain 120 volts of EMF.

Review

  1. When some of the components are connected parallel with each other, they form a parallel circuit.
  2. A voltmeter must be wired in parallel in a circuit in order to measure the difference in EMF from one point to another.