The circuit rules you've learned are based on two fundamental conservation laws:
Kirchhoff's Current Law (KCL): The total current entering any junction equals the total current leaving it. This is just conservation of charge — charge cannot be created or destroyed. In parallel circuits, the current splits but the total is conserved.
Kirchhoff's Voltage Law (KVL): The sum of all potential differences around any closed loop equals zero. This is just conservation of energy — energy given by the supply equals energy transferred by all components. In series circuits, the voltages add up to the supply voltage.
These laws apply to all circuits — simple or complex. When you solve a tricky mixed circuit in your GCSE exam, you're applying Kirchhoff's Laws whether you know it or not.
Quick Check: In a parallel circuit, the supply is 6 V. What is the voltage across each branch?
6 V across every branch. In a parallel circuit, voltage is the same across each branch and equals the supply voltage.
This how it works covers How It Works: Kirchhoff's Laws (The Rules Behind the Rules) within Series & Parallel Circuits for GCSE Physics. Revise Series & Parallel Circuits in Electricity for GCSE Physics with 20 exam-style questions and 30 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 8 of 16 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Series & Parallel Circuits
In a series circuit, what is true about the current at all points?
A student adds an extra lamp to a parallel circuit. Explain how this affects the total current from the supply and the brightness of the original lamps.