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Electric circuit symbols

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

Components

Some of the more common components are:

Switch

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

When the switch is open, there is a break in the circuit and current stops flowing.

Lamp

An electric current heats the filament in a bulb so that glows white hot and gives out light.

Fixed resistor

A resistor restricts or limits the flow of electrical current.

A fixed resistor has a resistance that does not change.

Variable resistor

Adjusting this resistor changes its resistance.

A variable resistor is used in some dimmer switches and volume controls.

Thermistor

The resistance of a thermistor depends on its temperature.

One type of thermistor is called an NTC thermistor (negative temperature coefficient).

At low temperatures, the NTC thermistor has a high resistance.

As the temperature increases, the resistance decreases.

A thermistor can be used in thermostats or heat activated fire alarms.

Light-dependent resistor (LDR)

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.

A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.

Semiconductor diode

A semiconductor is a class of material between a good conductor and an insulator.

Examples of semiconducting materials include silicon and germanium.

A semiconductor diode allows current to flow in one direction only.

Current will not flow in the other direction.

Diodes are used to convert an alternating current into a direct current.

Cell

A chemical reaction occurs inside a cell with chemical energy being converted to electrical energy.

A cell has a positive terminal and a negative terminal.