Current in Series & Parallel Circuits (WJEC GCSE Science (Double Award)): Revision Note

Current in Series & Parallel Circuits

Current 

• Current is the flow of charge (free electrons) per unit time, around the closed loop of a circuit

• The direction of conventional current is from positive to negative

• Current has the symbol I

Current in Series & Parallel

• A series circuit is a circuit that has only one loop, or one path that the electrons can take

• In a series circuit, the current has the same value at any point

  • This is because the electrons have only one path they can take

  • Therefore, the number of electrons passing a fixed point per unit time is the same at all locations 

• This means that all components in a series circuit have the same current

Current in a Series Circuit

The current is the same at each point in a series circuit

• The amount of current flowing around a series circuit depends on two things:

  • The voltage of the power source

  • The resistance of the components in the circuit

• Increasing the voltage of the power source drives more current around the circuit

  • So, decreasing the voltage of the power source reduces the current

• Increasing the number of components in the circuit increases the total resistance

  • Hence less current flows through the circuit

How Voltage and Resistance Affects Current in a Series Circuit

Current will increase if the voltage of the power supply increases, and decrease if the number of components increases (because there will be more resistance)

Current in Parallel Circuits

• A parallel circuit is a circuit that has two or more loops, or more than one path that the electrons can take

• In a parallel circuit, the current has different values at different points in the circuit

  • This is because the circuit branches

  • Therefore, the electrons have different paths they can take

• The sum of the current in the individual branches is equal to the total current before (and after) the branches

Current in a Parallel Circuit

The current splits at the branches in a parallel circuit

• The advantages of this kind of circuit are:

  • The components can be individually controlled, using their own switches

  • If one component stops working the others will continue to function

    • This is because the electrons can still flow around one closed loop even if the other loop is open 

Parallel Circuit with Switches Controlling Individual Components

Diagram showing two bulbs connected in parallel with switches controlling each individual bulb

Measuring Current 

• The amount of current flowing through a circuit is measured using an ammeter

• The unit for current is amps (amperes) which has the symbol A

• Ammeters should always be connected in series 

An Ammeter Connected in Series

An ammeter connected in series can be used to measure the current around a circuit