Properties of 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

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

Two lamps connected in series with an open switch and a cell.Two lamps connected in series with an open switch and a cell

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 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 sum of all the potential differences across the components in a series circuit is equal to the total potential difference across the power supply.

Parallel connections

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

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

Two lamps connected in parallel with an open switch and a cell.Two lamps connected in parallel with an open switch and a cell

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.

For a parallel circuit the current from the electrical supply is greater than the current in each branch. The sum of all the current in every branch is equal to the current from the electrical supply.

Question

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

Four circuit diagrams showing in parallel or in series.
Four circuit diagrams. The top two are connected in series, the bottom two in parallel.