Series and Parallel Connections

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Also see: Symbols and Circuit Diagrams



Connecting Components

There are two ways of connecting components:

Two lamps connected in series

In series so that each component has the same current.

The battery voltage is divided between the two lamps. Each lamp will have half the battery voltage if the lamps are identical.

Two lamps connected in parallel

In parallel so that each component has the same voltage.

Both lamps have the full battery voltage across them. The battery current is divided between the two lamps.

Most circuits contain a mixture of series and parallel connections

The terms series circuit and parallel circuit are sometimes used, but only the simplest of circuits are entirely one type or the other. It is better to refer to specific components and say they are connected in series or connected in parallel.

For example: the circuit shows a resistor and LED connected in series (on the right) and two lamps connected in parallel (in the centre). The switch is connected in series with the two lamps.

See Lamps in Parallel below for another example.

Circuit with series and parallel sections

A circuit with both series
and parallel connections.


Lamps in Series

If several lamps are connected in series they will all be switched on and off together by a switch connected anywhere in the circuit. The supply voltage is divided equally between the lamps (assuming they are all identical).

If one lamp blows all the lamps will go out because the circuit is broken.

Lamps in series

Lamps in Parallel

If several lamps are connected in parallel each one has the full supply voltage across it. The lamps may be switched on and off independently by connecting a switch in series with each lamp as shown in the circuit diagram. This arrangement is used to control the lamps in buildings.

This type of circuit is often called a parallel circuit but you can see that it is not really so simple - the switches are in series with the lamps, and it is these switch and lamp pairs that are connected in parallel.

Lamps in parallel

Switches in Series

If several on-off switches are connected in series they must all be closed (on) to complete the circuit.

The diagram shows a simple circuit with two switches connected in series to control a lamp.

Switch S1 AND Switch S2 must be closed to light the lamp.

Switches in series

Switches in Parallel

If several on-off switches are connected in parallel only one needs to be closed (on) to complete the circuit.

The diagram shows a simple circuit with two switches connected in parallel to control a lamp.

Switch S1 OR Switch S2 (or both of them) must be closed to light the lamp.

Switches in parallel

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