A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.
The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential (voltage); the component is an implementation of the same principle, hence its name.
They are commonly used to control electrical devices such as volume controls on audio equipment. It is operated by a mechanism can be used as position transducers, for example, in a joystick.
They are rarely used to directly control significant power (more than a watt), since the power dissipated in them would be comparable to the power in the controlled load.
Rotary potentiometer (the most common type) vary their resistive value as a result of an angular movement. Rotating a knob or dial attached to the shaft causes the internal wiper to sweep around a curved resistive element. The most common use of a rotary potentiometer is the volume-control pot.
Preset or trimmer potentiometers are small “set-and-forget” type potentiometers that allow for very fine or occasional adjustments to be easily made to a circuit, (e.g. for calibration). Single-turn rotary preset potentiometers are miniature versions of the standard variable resistor designed to be mounting directly on a printed circuit board and are adjusted by means of a small bladed screwdriver or similar plastic tool.
Slider potentiometers, or slide-pots, are designed to change the value of their contact resistance by means of a linear motion and as such there is a linear relationship between the position of the slider contact and the output resistance.
Slide potentiometers are mainly used in a large range of professional audio equipment such as studio mixers, faders, graphic equalizers and audio tone control consoles allowing the users to see from the position of the plastic square knob or finger-grip the actual setting of the slide.