Wire

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Jointed Wires

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Un-jointed Wires

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Cell

Supplies electrical energy.
The larger terminal (on the left) is positive (+). 
A single cell is often called a battery, but strictly a battery is two or more cells joined together.

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Battery

Supplies electrical energy. A battery is more than one cell.
The larger terminal (on the left) is positive (+).

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DC Power Supply

Supplies electrical energy.
DC = Direct Current, always flowing in one direction.

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AC Power Supply

Supplies electrical energy.
AC = Alternating Current, continually changing direction.

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Fuse

A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.

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Transformer

Two coils of wire linked by an iron core. Transformers are used to step up (increase) and step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is no electrical connection between the coils.

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Earth/Ground

0V 

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Lamp (lighting)

A transducer which converts electrical energy to light. This symbol is used for a lamp providing illumination, for example a car headlamp or torch bulb.

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Lamp (indecator)

A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator, for example a warning light on a car dashboard.

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Heater

A transducer which converts electrical energy to heat.

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Motor

A transducer which converts electrical energy to kinetic energy (motion).

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Bell

A transducer which converts electrical energy to sound.

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Buzzer

A transducer which converts electrical energy to sound.

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Inductor (Coil, Solenoid)

A coil of wire which creates a magnetic field when current passes through it. It may have an iron core inside the coil. It can be used as a transducer converting electrical energy to mechanical energy by pulling on something.

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Push Switch

(Push to Make)

A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell.

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Push-to-Break Switch

This type of push switch is normally closed (on), it is open (off) only when the button is pressed.

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On-Off Switch

(SPST)

Single Pole, Single Throw.
An on-off switch allows current to flow only when it is in the closed (on) position.

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2-Way Switch

SPDT

Single Pole, Double Throw.
A 2-way changeover switch directs the flow of current to one of two routes according to its position. Some SPDT switches have a central off position and are described as 'on-off-on'.

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 Dual On-Off Switch

(DPST)

Double Pole, Single Throw.
A dual on-off switch which is often used to switch mains electricity because it can isolate both the live and neutral connections.

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Resistor

A resistor restricts the flow of current, for example to limit the current passing through an LED. A resistor is used with a capacitor in a timing circuit. 

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Rheostat

(Variable Resistor)

This type of variable resistor with 2 contacts (a rheostat) is usually used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit.

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Potentiometer

(Variable Resistor)

This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal.

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Preset Variable Resistor

This type of variable resistor (a preset) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.

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Capacitor

A capacitor stores electric charge. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

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Polarized Capacitor

A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

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Variable Capacitor

A variable capacitor is used in a radio tuner.

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Diode

A device which only allows current to flow in one direction.

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L.ight E.mitting D.iode

A transducer which converts electrical energy to light.

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Transistor

(NPN)

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.

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Transistor

(PNP)

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.

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Microphone

A transducer which converts sound to electrical energy.

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Earphone

A transducer which converts electrical energy to sound.

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Speaker/Loudspeaker

A transducer which converts electrical energy to sound.

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Amplifier

An amplifier circuit with one input. Really it is a block diagram symbol because it represents a circuit rather than just one component.

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Antenna

(Aerial)

A device which is designed to receive or transmit radio signals.

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Relay

-NO Normally Open

 -COM Common

   -NC Normally Closed

An electrically operated switch, for example a 9V battery circuit connected to the coil can switch a 230V AC mains circuit.

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Voltmeter

used to measure voltage 
The proper name for voltage is 'potential difference'

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Ammeter

used to measure current

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Galvanometer

a sensitive meter which is used to measure tiny currents, usually 1mA or less.

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Ohmmeter

used to measure resistance

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Oscilloscope

used to display the shape of electrical signals and it can be used to measure their voltage and time period

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