Circuits
- Current only flows around a complete circuit. An open switch breaks the circuit.
- Components include cells, batteries (two or more cells), switches, bulbs (lamps), resistors, buzzers, motors, ammeters, voltmeters and LEDs. Each has a circuit symbol.
- Models help explain circuits: in the rope model, the cell is the person pulling the rope round, and the rope is the charge that moves everywhere at once. Charge isn't used up; energy is transferred.
Current
- Current is the flow of electric charge. It is measured in amps (A) with an ammeter connected in series.
- In a series circuit, the current is the same everywhere.
- In a parallel circuit, the current splits at a junction, and the currents in the branches add up to the total current.
Potential difference
- Potential difference (voltage) is the "push" from the cell. It is measured in volts (V) with a voltmeter connected in parallel, across a component.
- In a series circuit, the voltages across the components add up to the voltage of the supply.
- In a parallel circuit, each branch gets the full voltage of the supply.
Series and parallel circuits
- Series: one loop. If one bulb breaks, they all go out. Adding more bulbs makes each one dimmer.
- Parallel: several branches. If one bulb breaks, the others stay on, and each bulb is as bright as a single bulb would be. Homes are wired in parallel so that each light can be switched on and off separately.
- Conductors, such as copper, let current flow easily. Insulators, such as plastic and rubber, don't.
- When drawing conclusions, describe the pattern in the results, quote data, and explain it using science.
Key terms
- Circuit
- A complete loop that current can flow around.
- Current
- The flow of electric charge, measured in amps (A).
- Ammeter
- Measures current; connected in series.
- Potential difference
- The push that makes current flow, measured in volts (V).
- Voltmeter
- Measures potential difference; connected in parallel.
- Series circuit
- A circuit with all the components in one loop.
- Parallel circuit
- A circuit with more than one branch.
- Cell
- A single source of electrical energy.
- Battery
- Two or more cells joined together.
- Switch
- A component that opens or closes a circuit.
- Electrical conductor
- A material that lets current flow easily.
- Electrical insulator
- A material that doesn't let current flow easily.