Circuit elements


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 common components are:


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


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

Fixed resistor

A resistor restricts or limits the flow of electrical curent. A fixed resistor has a resistance that does not change.

Variable resistor

Moving the position of the slider on this resistor, changes the resistance. A variable resistor is used in some dimmer switches and volume controls.


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.

Light-dependent resistor (LDR)

The resistance of an 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 automatic lights that come on when it gets dark.

Semiconductor diode

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 (ac) into a direct current (dc).