KS3 Physics

Motion and Forces
Waves
Matter

Series Circuits

A series circuit is a circuit in which all the components are in the same loop. An example of this is the circuit diagram below.

As you can see, both lamps and the cell are in the same loop of wire. You can add as many components as you want to the series circuit, but it would have to be in the same loop as the other components. The component you add does not have to be a lamp, it could be a resistor, a motor or any other component.

The current in a series circuit depends on the number of cells.; the more cells there are, the higher the current will be.

However, a disadvantage to series circuits is that when a component breaks, it breaks the circuit. This means the other components will no longer work.

In the series circuit diagram shown above, both lamps are lit because all components are functioning properly. However, if one of the lamps broke, it would break the whole circuit and none of the lamps would light up.

It doesn’t matter which component breaks in a series circuit, as all components are in the same loop. So, when one component breaks, none of the other components work.

Current in a Series Circuit

In a series circuit, the current is the same at every point in the circuit. We measure the current using an ammeter, which is placed in series with the components.

• Current is measured in amperes (A).

As you can see in the diagram below, ammeters can be placed anywhere in the circuit.

If we were to take readings at each ammeter, we would see that the current is the same at each point.

Between the lamps, the current reads 3 amperes, and the same 3-ampere current is found on both sides of the cell.

Rules About Potential Difference in a Series Circuit

In a series circuit, the potential difference is shared between the components. The sum of the potential differences across all components is equal to the potential difference of the cell or battery.

We use a voltmeter to measure the potential difference.

• Potential difference is measured in volts (V).

In either a series or a parallel circuit, the voltmeter is not placed in the same loop as the other components. Instead, it is placed parallel to the component you are measuring, connecting a wire to either side of the component you are measuring. You can see this in the series circuit diagram below.

If we were to take the readings at each voltmeter, we would see that the potential difference is shared between the components.

At the top, we can see the potential difference the cell provides is 4 V. As we have two of the same components, being the two lamps, the potential difference is shared equally between the components. The 2 V across the two lamps adds up to the 4 V provided by the cell.

Let’s look at a series circuit diagram with different components.

Since the diagram includes both a lamp and a resistor, we now have different types of components. This means the potential difference provided by the cell might be distributed unequally. In this case, the potential difference across the resistor is 3 V and the potential difference across the lamp is 1 V

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