A series circuit is a circuit in which all of 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 has 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.
Electrons must pass through all components in a series circuit. So, when a component breaks, it breaks the circuit. This means that the other components will no longer work.
The current in a series circuit depends on the number of cells. Increasing the number of cells increases the current.
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.
As you can see in the diagram below, ammeters can be placed anywhere in the circuit.
If we took readings at each ammeter, we would see that the current is the same at each point.
Between the lamps, the current is 3 amperes and the current on both sides of the cell is 3 amperes.
In a series circuit, the potential difference is shared between the components. The sum of potential differences across all of the components is equal to the potential difference across the cell or battery. So we can say:
Vtotal = V1 + V2 + V3…
For example, If we took 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 that the cell provides is 4 V. As we have two of the same components, being the 2 lamps, the potential difference is shared equally between the components. The 2 V across the two lamps adds up to the 4 V, which is provided by the cell.
When resistors are connected in series, we must add up all of the resistances together. This is because the current has to flow through each resistor. Which means:
Rtotal = R1 + R2
In other words, the total resistance is equal to the sum of the individual resistances.