Currents in Electrical Circuits

Most cells produce a potential difference measuring 1.5 V. If two or more cells are connected in series in a circuit then their potential difference is the sum of their potential differences. The more cells there are in a circuit the larger the current flowing and so more current will flow through the components.

However, they need to be connected in the same direction. If not, and they’re in series but facing opposite directions, then the potential difference will be 0 V which means they’ll be no current.

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Circuit diagrams

In order for a circuit to work:

• – the circuit must be complete
• – there can’t be any short circuits

If a circuit is complete then you should be able to follow the wire coming out of the battery through the lamp and then back to the battery.

A short circuit means that the light won’t turn on. If there’s a way of moving through the lamp without moving through any other components then there’s a short circuit.

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Series connection

If the components in a circuit diagram are connected in a loop one after the other then they’re said to be connected in series. The current which flows through each component is the same.

If one bulb was to break then the other wouldn’t light either because the current is travelling in a loop and so wouldn’t be able to reach it. There’s only one route the charge can take around the circuit.

The current is dependent on supply’s potential difference and the circuit’s total resistance:

current = potential difference of supply / total resistance

In a series circuit the components share the potential difference. So, the sum of the potential differences of each component is the potential difference of the supply. It’s the same for the resistance: the sum of the resistance of each component is the total resistance. The larger the resistance of one of the components then the bigger the share is of the total supply of potential difference.

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Parallel connection

If components are connected on separate loops then they’re said to be connected in parallel. Instead of each component receiving the same amount of current, the current is shared between each component.

If one bulb breaks in this circuit then the other bulb will still be able to function. This is because all the components in the circuit are connected across the supply potential difference so their potential differences are the same.

The components act like junctions so the current can change as different amounts of charge can flow through them. The amount of current flowing through a component depends on its resistance: the larger the resistance the the smaller the charge. The total current flowing through the circuit can be calculated by summing the current flowing through each component.