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Home > Physics > Using electricity > Useful circuits


Useful circuits


It is important that you know about current and voltage in series and parallel circuits. This revision bite will take you through series and parallel circuits, current in series circuits, current in parallel circuits, voltage across components in a series circuit, voltage across components in a parallel circuit and resistors in series and parallel circuits.

Work through them all or go to the ones that interest you. You may wish to print a hard copy for your reference.

Series and parallel circuits

You should be able to recognise series and parallel circuits.

A series circuit where there is only one path for the current - contains a cell, switch and lamp all in series with one another.

In a series circuit there is only one path for the current and the current is the same at all points. Here is an example of such a circuit.

Parellel circuit with two lamps in parallel, and a cell and switch.

In a parallel circuit there is more than one path for the current to follow. At some points in a parallel circuit there will be junctions of conductors. Junctions are shown by dots on circuit diagrams. The sum of currents in parallel branches is equal to the current drawn from the supply. This circuit shows two lamps in parallel.

Parellel circuit with switches in parallel, a lamp, and a cell.

Some parallel circuits have switches in parallel, as the circuit shown here.

Try this question


Which circuit shows:

  • resistors in series?
  • resistors in parallel?
  • switches in series?
  • switches in parallel?

A circuit with switches in series - a cell followed by 2 switches, followed by resistor, followed by switch, all in series.
A circuit with switches in parallel with a lamp and cell. The lamp and cell are in series with each other.

A circuit with resistors in parallel. There is a cell and switch in series with one another which is in parallel to the resistors.
A circuit with 2 resistors, a switch and a cell in series.
  • Circuit 1 has switches in series.
  • Circuit 2 has switches in parallel.
  • Circuit 3 has resistors in parallel.
  • Circuit 4 has resistors in series.


A picture of an electrical circuit.

Class Clips

Video clip about resistors and transistors in circuits.

Watch the following video clips to learn more about circuits:

The importance of circuits

How an electric circuit works

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