Circuit symbols

Switch (open)

Used to turn a circuit off

Switch (closed)

Used to turn a circuit on

Cell (electrical)

Provides the energy for a circuit

Battery

Two or more cells connected together

Diode

A device that allows current to flow in one direction only

Resistor (fixed)

A device that restricts or limits the flow of current

Variable resistor

A device that has a slider which can be moved to change the resistance

LED (light-emitting diode)

A diode which emits light and is much more efficient than a filament bulb

Lamp (filament bulb)

A device containing a filament in a bulb that heats up when a current flows so that it emits light

Fuse

A safety device consisting of a strip of wire that melts, breaking an electric circuit, if too much current passes through it

Voltmeter

A device placed in parallel with a component to measure the potential difference (voltage) across it

Ammeter

A device placed in series with a component to measure the current through it

Thermistor

A device whose resistance decreases as the surrounding temperature increases

LDR (light-dependent resistor)

A device whose resistance decreases as the surrounding light intensity increases