A potentiometer, sometimes called a pot or potmeter, is a three-terminal variable resistor wherein the resistance is manually varied to control the flow of electrical current. In essence, a potentiometer acts as an adjustable voltage divider. They are considered a passive electronic component and operate by altering the position of a sliding contact across a uniform resistance. In a potentiometer, the entire input voltage is applied across the entire length of the resistor, and the output voltage is determined by voltage drop between the fixed and sliding contacts.
In a potentiometer, the two terminals of the input source are fixed to the end of the resistor. To adjust the output voltage regulator, the sliding contact is moved along the output side of the resistor. This differs from a rheostat, in which one end is fixed and the sliding terminal is connected to the circuit. Potentiometers are very basic instruments used for comparing the electromotive force of two cells for calibrating ammeters, voltmeters, and watt-meters.
The working principle of potentiometers is relatively simple. For example, imagine two batteries are connected parallelly through a galvanometer. The negative battery terminals are connected to each other, as are the positive battery terminals. If the electrical potential of both battery cells is the same, there is no current circulating through the circuit and the galvanometer will show no deflection. The operation of a potentiometer is based on this phenomenon.
There are two main types of potentiometers: rotary and linear. While they both operate in roughly the same way, the structural features of the two types differ. It’s also important to note that rotary and linear potentiometers are examples of DC potentiometers, and AC potentiometers are slightly different.
Rotary potentiometers are primarily used to obtain adjustable supply voltage to a part of an electrical circuit. A common example of a rotary potentiometer is the volume controller of a transistor radio. Rotary potentiometers feature two terminal contacts and a uniform resistance placed between them in a semi-circular pattern. The device also has a middle terminal connected to the resistance via a sliding contact attached with a rotary knob. By rotating, the knob moves the sliding contact on the semi-circular resistance. The voltage is taken between the resistance end contact and the sliding contact.
Linear potentiometers are relatively similar, the only main difference being that the sliding contact’s movement along the resistor is linear, rather than rotary. In linear potentiometers, the two ends of a straight resistor are connected across the source voltage. A sliding contact can be slid on the resistor along a track attached to the resistor. The terminal connected to the sliding contact is connected to one end of the output circuit and one of the terminals of the resistor is connected to the opposite end of the output circuit. Linear potentiometers are primarily used to measure the voltage across a branch of a circuit, to measure the internal resistance of a battery cell, or to compare a battery cell with a standard cell. In more common everyday applications, they are used in the equalizer of sound mixing systems.
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