Electricity and circuits
Building circuits, circuit symbols, conductors and insulators, and how changing a circuit changes how it works.
📌 Key points
- A circuit needs a complete loop with no gaps and a source of electricity, such as a cell.
- A switch opens or closes a gap in a circuit. When the switch is open, there is a gap and no current flows.
- Circuits are drawn with symbols for a cell, battery, lamp (bulb), switch, buzzer, motor and wires.
- Electrical conductors, such as copper and other metals, let electricity flow. Insulators, such as plastic, rubber, wood and glass, do not.
- Wires are made of copper (a conductor) covered in plastic (an insulator) to keep us safe.
- Adding more cells makes a bulb brighter, a buzzer louder and a motor spin faster.
- Adding more bulbs to a single loop (a series circuit) makes each bulb dimmer.
- In a series circuit, if one bulb breaks, the loop is broken and all the other bulbs go out.
- Mains electricity is much more dangerous than cells. Never touch plugs or sockets with wet hands or push things into sockets.
📖 Key words
- Circuit
- A complete loop that electricity can flow around.
- Cell
- A single unit that pushes electricity around a circuit (often called a battery).
- Battery
- Two or more cells joined together.
- Switch
- A component that opens or closes a gap in a circuit.
- Series circuit
- A circuit where all the components are in one single loop.
- Current
- The flow of electricity around a circuit.
- Electrical conductor
- A material that lets electricity flow through it.
✏️ Worked example
A circuit has one cell, a closed switch and one bulb. What happens to the bulb if (a) a second cell is added, or (b) a second bulb is added to the loop instead?
- (a) Two cells push more current around the circuit, so the bulb becomes brighter.
- (b) Two bulbs make it harder for the current to flow, so less current flows and both bulbs are dimmer.
- In both cases the loop must stay complete. If the switch is opened, nothing lights.
- Answer: (a) brighter, (b) dimmer.
Trace the loop with your finger before you answer. Any gap or open switch means nothing in that loop works.
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