Series and parallel circuits

The components in electrical circuits can be connected in series or in parallel.

Series connections

Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows through each component connected in series is the same.

Two lamps connected in series

Circuit diagram with one battery, one switch and two lamps connected in series.Two lamps connected in series with an open switch and a cell

The circuit diagram shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light.

Series circuits are useful if you want a warning that one of the components in the circuit has failed. For example, a circuit breaker or a fuse must be connected in series in order for it to work. If Christmas tree lights all go out when one bulb breaks, they are connected in series.

The current is the same throughout a circuit and voltages add up to the supply voltage.

Parallel circuits

Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel. The total amount of current flowing into the junction, or split, is equal to the total current flowing out. The current is described as being conserved.

Two lamps connected in parallel

Circuit diagram with one battery, one switch and two lamps connected in parallel.Two lamps connected in parallel with an open switch and a cell

The circuit diagram shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light.

The lights in most houses are connected in parallel. This means that they all receive the full voltage and if one bulb breaks the others remain on.

In parallel circuits, the voltage is the same across each branch and is equal to the supply voltage. The sum of the currents in each branch is equal to the current in the supply.

Question

Which of the circuits here are connected in series, and which are connected in parallel?

4 circuit diagrams labelled A,B,C and D. A has one lamp. B has two lamps connected series. C has two lamps connected in parallel. D has two lamps connected in parallel.

A = series

B = series

C = parallel

D = parallel

curriculum-key-fact
The wiring in a house connects all appliances together in parallel. This is so that each has the mains supply of 230 volts across it and also so that they can all be used independently.