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variable resistor

An electronic component that is used to vary the amount of current that flows through a circuit. It works by sliding a wiper terminal across a resistive material, typically a thin film or chunk of carbon or a resistive wire made of nickel chromium or tungsten alloys. After being set to the appropriate location, the wiper's position often remains fixed on the circuit board; however, it can also be made user adjustable with a screwdriver.

Pots and Rheostats
Potentiometers and rheostats are variable resistors in which the wiper terminals take the form of a dial or slider that the user does manipulate, such as the volume control of a radio or music system. A rheostat is similar to a potentiometer, but handles more power. See resistor.

Variable Resistor
As the wiper is moved across the body of the device, the resistance increases between the wiper terminal and one end terminal and decreases between the wiper and the other end. (Image courtesy of Alltronics,

A Potentiometer
Potentiometers are variable resistors commonly used to control the volume on a radio or music system. In this example, the dial controls the wiper in the device.


An electronic component that resists the flow of current in an electronic circuit. Resistors are often made out of chunks of carbon or thin films of carbon or other resistive materials. They can also be made of wires wound around a cylinder. The common resistor is a two-wire package with a fixed resistance measured in ohms; however, different types of resistors are adjustable by the circuit designer or the user (see variable resistor).

Discrete or IC
Discrete resistors are individual packages. On a circuit board, discrete axial resistors are commonly used with their two wires soldered into the holes of the board. Generally smaller than axial resistors, discrete surface-mounted resistors are soldered on top of the board. In addition, resistors are built into microprocessors and other integrated circuits (ICs), but they use semiconductor structures for their fabrication in a manner similar to transistors and PN junctions. See variable resistor and thru-hole.

There are a wide variety of resistors in use. The chip in the center is a reminder that resistive elements are also used in integrated circuits.

Axial Resistors
Axial resistors are discrete components with wire leads that are soldered to other components or to the circuit board. This type of resistor is easily identified by its color bands, which indicate its resistance and tolerance (see example below).

The color bands on these resistors are interpreted as 3-3-0000-5%, which means 330,000 ohm resistors, plus or minus 5%.

Surface Mount Resistors
Surface mount resistors are soldered on top of the circuit board and are identified by number rather than color bands.

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