Potentiometers are versatile electronic components used to change the resistance in a circuit. Like resistors with a fixed value, they're used to control the flow of current through a circuit. However, potentiometers can be adjusted to increase or decrease the flow of current dynamically. They're widely used in audio equipment, electronics and even household wiring, though the potentiometers used for audio purposes work differently from most others.
Potentiometers can use a variety of materials, but they all work in much the same way. When the control is moved, contacts within the potentiometer are either separated or brought closer together. Electricity flows between the two terminals along a strip of resistive material. The further apart the terminals are, the more resistance -- measured in ohms -- is introduced into the circuit. In early potentiometers, the strip of resistive material was often thicker at one end, then tapered toward the other. For that reason, a potentiometer's change of resistance is often referred to as its "taper." There are two broad categories, linear and logarithmic.
Chances are, you won't have to look far to find a potentiometer. If the chandelier over your dining table has a dimmer, that's a potentiometer. The dial or sliding switch that controls the speed of your stand mixer is a potentiometer. So is the control that brightens or dims the dash lights in most older cars, and the color and vertical hold knobs on elderly televisions. Another common use of potentiometers, one of the most visible for consumer purposes, is in volume controls. Potentiometers used for general applications usually have a linear taper, while those for audio purposes typically have a logarithmic taper.
Linear vs. Audio
Potentiometers, or "pots" to electronics enthusiasts, are differentiated by how quickly their resistance changes. In linear pots, the amount of resistance changes in a direct pattern. If you turn or slide it halfway, its resistance will be halfway between its minimum and maximum settings. That's ideal for controlling lights or a fan, but not for audio controls. Volume controls have to cater to the human ear, which isn't linear. Instead, logarithmic pots increase their resistance on a curve. At the halfway point volume will still be moderate, but it will increase sharply as you keep turning up the volume. This corresponds to how the human ear hears.
For home hobbyists and handymen, potentiometers have multiple uses. Your local building-supplies store carries sliding and rotating dimmer switches to control your room's lighting. Electronics retailers such as RadioShack carry both linear and logarithmic pots in in a variety of sizes and shapes to suit most common projects. If you're learning to make basic circuits, use a small board-mounted linear pot to control the speed of an electric motor. With a larger logarithmic pot, you can replace the volume control on your guitar. Some pots come premounted in electrical boxes, for use as in-wall volume controls for a home's prewired speaker system.
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