Standard symbols

Electric circuit symbols

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

Circuit symbols of open switch, closed switch, lamp, voltmeter, resistor, variable resistor, diode, light emitting diode, battery, cell, ammeter, fuse, thermistor and light dependant resistor.

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.

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.
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