A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider.

Contamination can potentially enter anywhere along the slot the slider moves in, making effective sealing more difficult and compromising long-term reliability.

Other materials used include resistance wire, carbon particles in plastic, and a ceramic/metal mixture called cermet.

Some multiturn potentiometers have a linear resistive element with a sliding contact moved by a lead screw; others have a helical resistive element and a wiper that turns through 10, 20, or more complete revolutions, moving along the helix as it rotates.

User-accessible rotary potentiometers can be fitted with a switch which operates usually at the anti-clockwise extreme of rotation.

Multiple resistance elements can be ganged together with their sliding contacts on the same shaft, for example in stereo audio amplifiers for volume control.

In other applications, such as domestic light dimmers, the normal usage pattern is best satisfied if the potentiometer remains set at its current position, so the switch is operated by a push action, alternately on and off, by axial presses of the knob.

They are usually called "trimmer", "trim[ming]", or "preset" potentiometers (or pots), or the genericized brand name "trimpot".

When a percentage is referenced with a non-linear taper, it relates to the resistance value at the midpoint of the shaft rotation.

The resistive element is designed to follow a logarithmic taper, aka a mathematical exponent or "squared" profile.

The two resistive tracks overlap at approximately 50% of the potentiometer rotation; this gives a stepwise logarithmic taper.

Unlike mechanical potentiometers, non-contact potentiometers use an optical disk to trigger an infrared sensor, or a magnet to trigger a magnetic sensor (as long as there are other types of sensors, such as capacitive, other types of non-contact potentiometers can probably be built), and then an electronic circuit does the signal processing to provide an output signal that can be analogue or digital.

However, absolute encoders must also use similar principles, although being for industrial use, certainly the cost must be unfeasible for use in domestic appliances.

The word rheostat was coined in 1843 by Sir Charles Wheatstone,[7] from the Greek ῥέος rheos meaning "stream", and -στάτης -states (from ἱστάναι histanai, "to set, to cause to stand") meaning "setter, regulating device",[8][9][10] which is a two-terminal variable resistor.

For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper.

The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point.

Carbon-pile rheostats are used as load banks for testing automobile batteries and power supplies.

A digipot is generally immune to the effects of moderate long-term mechanical vibration or environmental contamination, to the same extent as other semiconductor devices, and can be secured electronically against unauthorised tampering by protecting the access to its programming inputs by various means.

In equipment which has a microprocessor, FPGA or other functional logic which can store settings and reload them to the "potentiometer" every time the equipment is powered up, a multiplying DAC can be used in place of a digipot, and this can offer higher setting resolution, less drift with temperature, and more operational flexibility.

[11] For touch-screen devices using resistive technology, a two-dimensional membrane potentiometer provides x and y coordinates.

Another is that the sensor requires occasional calibration to match touch location to the underlying display.

(Capacitive sensors require no calibration or contact force, only proximity of a finger or other conductive object.

The widespread use of potentiometers in consumer electronics declined in the 1990s, with rotary incremental encoders, up/down push-buttons, and other digital controls now more common.

The 'log pot', that is, a potentiometer has a resistance, taper, or, "curve" (or law) of a logarithmic (log) form, is used as the volume control in audio power amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is approximately logarithmic.

A potentiometer was often used to adjust "vertical hold", which affected the synchronization between the receiver's internal sweep circuit (sometimes a multivibrator) and the received picture signal, along with other things such as audio-video carrier offset, tuning frequency (for push-button sets) and so on.

Potentiometers can be used as position feedback devices in order to create closed-loop control, such as in a servomechanism.

Potentiometers are also very widely used as a part of displacement transducers because of the simplicity of construction and because they can give a large output signal.

In analog computers, high precision potentiometers are used to scale intermediate results by desired constant factors, or to set initial conditions for a calculation.

If RL is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation:

Because of the load resistance, however, it will actually be slightly lower: ≈ 6.623 V. One of the advantages of the potential divider compared to a variable resistor in series with the source is that, while variable resistors have a maximum resistance where some current will always flow, dividers are able to vary the output voltage from maximum (VS) to ground (zero volts) as the wiper moves from one end of the potentiometer to the other.