What is a Potentiometer? - Definition & Types

Instructor: Raghav Mahalingam

Raghav has a graduate degree in Engineering and 20 years of professional experience.

This lesson defines a potentiometer and a method to calculate the voltage output of a potentiometer. Two main types of potentiometers are discussed, linear and rotary, with some details on their construction.

Let's Divide up the Cake!

Imagine you have a big rectangular slab of a cake and want to store it for later. However, you don't have a box big enough for the cake. You take a knife and slice the cake at exactly the right location so it will fit in the box. The rest of the cake could get eaten or stored in another box! Also, it's possible to cut the cake to any size box that you want!

A potentiometer does the job of the knife in the above example. Imagine you only have 9 V battery, but you need 1.5 V to power an appliance. A potentiometer takes the 9 V and splits it into 1.5 V and 7.5 V, so that you can use the 1.5 V that you need.

Definition of a Potentiometer

Before we define a potentiometer, let's quickly look at what a resistor is. A resistor is a basic two-terminal electrical element that resists the flow of electric current when a voltage is applied across the two terminals. The value of the resistance determines how much current flows, depending on the voltage applied across the terminals, and is given by Ohm's Law as I = V/R.

Figure 1. Two terminal resistor

Now imagine there is a way to add a third terminal to the resistor that can be moved around. Adding a moving third terminal converts the resistor into a potentiometer. Therefore, a potentiometer can be defined as a three-terminal resistor with a variable or moving contact that divides a voltage into two parts. This is shown schematically in the figure below.

Figure 2. Schematic of a potentiometer

As seen in Figure 2, the moving terminal splits the voltage V into V1 and (V-V1). If the resistance of the element up to the moving terminal is R1, then,

V1 = V x R1/R

For example, assume a voltage input of 10 V is supplied to a potentiometer with a total resistance 100 k-Ohm, and the resistance from the stationary terminal to the wiper is 30 k-Ohm. The output voltage of the potentiometer will read,

V1 = 10 * 30/100 = 3 V

Types and Uses of Potentiometers

Potentiometers can be of two types, linear and rotary. The difference between the two is in the mechanical construction of the potentiometer. A potentiometer consists of four main components: two fixed terminals, one moving terminal (called the wiper), a resistive strip or track, and the housing. For both the linear and rotary potentiometer, the third terminal or wiper slides over the resistive element and depending on the location of the wiper, the output voltage changes. The only difference between the two types of potentiometers is that for a linear potentiometer the resistive strip is arranged on a straight track, while in a rotary potentiometer the resistive strip is arranged in a circular track.

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