1A complete circuit
Current only flows round a complete circuit: an unbroken loop from one end of the cell, through the lamp, and back to the other end.
complete circuit
Lesson 6.1 notes
Circuits, conductors and insulators
Complete circuits, current as a flow of charge, circuit symbols, switches, and conductors and insulators.
2A flow of charge
An electric current is a flow of charge. In metal wires the charge is carried by tiny electrons, which the cell pushes round the circuit.
currentelectron
3Like a loop of rope
Like a loop of rope, the charge all round the circuit moves at the same moment. It isn't used up: the same amount comes back to the cell.
4Circuit symbols
Each component has a standard symbol, so anyone in the world can read a circuit diagram.
symbol
5Circuit diagrams
A circuit diagram uses symbols and straight wires with square corners. On a cell symbol, the long thin line is the positive (+) side.
circuit diagram
6Switches
A switch makes or breaks the circuit. Closed: no gap, so current flows and the lamp lights. Open: a gap, so no current flows.
closedopen
7Conductors and insulators
Conductors, such as all metals and graphite, let current flow easily. Insulators, such as plastic, wood, rubber and glass, hardly let any flow.
conductorinsulator
Explore: Conductor tester
Put different materials across the gap in a circuit and close the switch. Which ones let the lamp light?
Common mistake: A closed switch means the circuit is on
It sounds backwards, but closing a switch closes the gap, so current can flow and the lamp lights. An open switch leaves a gap, so no current flows.
Remember
- Current is a flow of charge, measured in amps (A). In metal wires the charge is carried by electrons.
- Current only flows round a complete circuit. A closed switch completes the circuit; an open switch breaks it.
- Metals and graphite are conductors. Plastic, wood, rubber and glass are insulators.
Going further at GCSE
GCSE: Circuit symbols and switches → GCSE: Current and charge →