The diagram below shows a simple, but slightly more realistic, parallel circuit:



In parallel circuits, components or groups of components reside on their own particular branch. Parallel circuits have far more uses than series circuits and are therefore more widely encountered.


In the example above we have a 12 V cell with an ammeter connected in series (an ammeter is always connected in series in circuits) and three identical filament lamps on their own individual branches, individually switched. There is a "master" switch to the left of the cell which will control the whole circuit and finally a voltmeter across the third lamp (note, voltmeters are always connected in parallel that is "across" the component being tested).


If the master switch is closed, nothing will happen because all of the lamps are individually switched, but when one of the individual lamps has its switch closed it will illuminate.


Closing the individual switches of the other two lamps will mean that all of the lamps will stay on because in parallel circuits the potential difference is identical to that of the cell across every branch in the circuit, so the potential difference across lamp number one will be the same as that across lamp number two, and the same as that across lamp number three ie: 12 V, because each branch of the circuit forms its own complete closed-loop from one end power supply to the other.


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