Electricity > Component Identification

This page may help you identify certain electrical components. Alongside a typical photograph of the component is a description of its properties and uses.

Typical appearance	Component name	Description and uses
	LDR (light dependent resistor)	Also may be known as a photoresistor. An LDR's resistance decreases with increasing light intensity and so can be used in light sensors security alarms.
	Resistor	Resistors are two terminal components used in the majority of electrical appliances. The electrical resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. Essentially a resister 'resists' the flow of electrical current, dropping the voltage to a specific level.
	Relay	A relay is a switch which opens and closes under the control of another circuit, using an electromagnet to mechanically switch the circuit on or off. Often used to control an output circuit of higher power. For example, it may only take 9V to operate the relay which in turn may switch a 240V circuit.
	Transistor	Transistors are used to amplify or switch electronic signals and are commonplace in modern computers. Transistors allow a small current or voltage to control the flow of a much larger current.
	Potentiometer	Also known as variable resistors, rheostats or pots. A potentiometer is a three-terminal resistor with a sliding contact which can select various voltages. Used to control volume or levels of low power. The sliding contact may be arranged in a linear or circular shape.
	Thermistor	A thermistor is a type of resistor with resistance varying with temperature. Often used to regulate temperatures in ovens and heating systems. Thermal fuses, often seen in labpacks contain thermistors which act as a switch, turning off an appliance if it overheats.
	Capacitor	Capacitors are components which can store energy within the electric field between two plates. Capacitors can therefore be charged and discharged. Also may be known as condensers, especially in vehicle circuits. Used as energy storing components.
	Diode	A diode is a component which allows current to flow one way through it but not the other. Used in rectifying circuits to convert AC to DC.
	LED (light emitting diode)	LEDs are semiconductor diodes which emit light. They are being used more and more due to their energy efficiency and plummeting cost to produce. The longer lead denotes the Anode (+) and must be connected the correct way around in a circuit.
	Fuse	A fuse usually consists of a fine metal wire contained within a glass chamber. They are used to protect the circuit from excessive current. The wire melts at the point where too much current flows. The break point is denoted by the 'rated current' displayed on the fuse in Amps.
	Reed switch	Reed switches consist of two metal contacts within a glass envelope. When introduced into a magnetic field the contacts either open or close which completes or breaks the circuit. Used in burglar alarms and proximity switches.