Science · Physics foundations
Simple circuits
Series and parallel.
What is an electric circuit?
A circuit is a complete loop that electricity can flow around. You need a power source (like a battery), wires, and components (like bulbs or buzzers). If the loop is broken, electricity stops flowing and components switch off.
Series circuits
In a series circuit, components are connected one after another in a single loop. Electricity has only one path to follow. If one bulb breaks, the whole circuit stops working because the loop is broken.
Parallel circuits
In a parallel circuit, components are connected on separate branches. Electricity can follow different paths at the same time. If one bulb breaks, the others keep working because electricity can still flow through other branches.
Comparing brightness and current
In series, bulbs share the battery's energy so they glow dimmer. Adding more bulbs makes them even dimmer. In parallel, each bulb gets the full battery voltage so they shine brighter. Each branch draws current independently.
Switches in circuits
A switch in a series circuit controls everything in that loop. A switch in one branch of a parallel circuit only controls components in that branch. Other branches keep working independently.
Finding related videos…
Worked examples
1. You build a circuit with two bulbs in series and one battery. One bulb unscrews. What happens?
- In a series circuit, components form one continuous loop.
- Unscrewing a bulb breaks the loop, so no electricity can flow.
- Both bulbs go out because the circuit is incomplete.
2. You connect three bulbs in parallel to one battery. How does their brightness compare to one bulb alone?
- Each bulb is on its own branch in a parallel circuit.
- Each bulb receives the full battery voltage independently.
- All three bulbs shine with the same brightness as one bulb alone would.
3. A circuit has two bulbs in series. You add a third bulb in series. What happens to brightness?
- The battery's voltage is now shared among three bulbs instead of two.
- Each bulb receives less voltage than before.
- All three bulbs glow dimmer than the original two did.
Try it yourself
Draw or describe a parallel circuit with one battery, two bulbs, and one switch that controls only one bulb.
Ready to test yourself?
Take a short topic test — every question maps to a syllabus point so you’ll see exactly which parts you’ve mastered.