What happens when you rotate a potentiometer knob?
Rotary potentiometers are three-terminal resistance devices. The outer two terminals are connected to each end of a resistance path – which could be carbon, conductive plastic, or wire-wound – whose resistance value gives the rating of the device. The middle terminal is connected to a wiper which is also mechanically connected to the control knob. As the control knob is rotated, the wiper moves along the resistance track.
If the external circuit is connected across the wiper and one end contact, the potentiometer acts as a rheostat or variable resistor. The series resistance in the external circuit varies as the potentiometer knob is rotated. Alternatively, if all three terminals are used, the potentiometer acts as a potential divider. For example, if the resistance track is connected between supply and ground, the voltage on the wiper varies as the potentiometer knob is turned. This voltage could be fed to the base of a transistor to control the sound level of an audio amplifier.
Note that a single-turn rotary potentiometer typically has less than 300 degrees of angular movement. Multi-turn potentiometers allow for a shaft rotation of more than 360 degrees of mechanical travel from one end of the resistive track to the other. Multi-turn pots are more expensive, but very stable with high precision used mainly for trimming and precision adjustments. The two most common multi-turn rotary potentiometers are the 3-turn (1080°) and 10-turn (3600°) types, but 5-turn, 20-turn and higher 25-turn pots are available in a variety of ohmic values.
