Circuit symbols

Symbols

The following symbols show the different components that can be found in an electrical circuit.

Individual circuit symbols in one sheet including, open switch, closed switch, lamp, voltmeter, ammeter, resistor, variable resistor, LDR, thermistor, diode, LED, cell, battery and fuse.

Some of the more common components are:

Switch

Lamp

A switch is used to turn a circuit on (closed switch) and off (open switch).

An electrical current heats the filament in a bulb so that it gives out light.

Fixed resistor

Variable resistor

A resistor limits the passage of electrical current. A fixed resistor has a resistance that does not change.

The resistance of this resistor is changed by moving the position of a slider. A variable resistor is used in some dimmer switches and volume controls.

Thermistor

Light-dependent resistor (LDR)

The resistance of a thermistor depends on its temperature. At low temperatures, the thermistor has a high resistance. As the temperature increases, the resistance decreases. A thermistor can be used in thermostats or heat-activated fire alarms.

The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases. An LDR can be used as a sensor in cameras or in security lights that come on automatically when it gets dark.

Diode

A diode allows current to flow in one direction only. Diodes are used to convert an alternating current into a direct current.