Current in Series & Parallel (Edexcel IGCSE Physics: Double Science)

• There are two ways of joining electrical components:
  • in series
  • in parallel

Current in series

• 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

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

• The amount of current flowing in a series circuit depends on:
  • the voltage of the power source
  • the number (and type) of components

• 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

Increasing the voltage and number of components in series

Current will increase if the voltage of the power supply increases and decreases if the number of components increases

• A parallel circuit is a circuit that has two or more loops, or more than one path that electrons can take
• Parallel circuits contain junctions and branches
  • Junctions are points where two or more wires meet to form a new branch
  • Branches are the sections of wire between junctions

Current in parallel

• In a parallel circuit, the current has different values at different points in the circuit
  • This is because the current splits at a junction
  • 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 splits at a junction into individual branches

Why is current conserved at a junction in a circuit?

• At a junction, the current is always conserved
  • This means the amount of current flowing into the junction is equal to the amount of current flowing out of it
  • This is because the charge is conserved

• Current does not always split equally – often there will be more current in some branches than in others
  • The current in each branch will only be identical if the resistance of the components along each branch is identical

• Current behaves in this way because it is the flow of electrons:
  • Electrons, or any charge, cannot be created or destroyed
  • This means the total number of electrons (and hence current) going around a circuit must remain the same
  • When the electrons reach a junction, however, some of them will go one way and the rest will go the other