As far as we know, resistors should always have two terminals; however, why does a potentiometer have three terminals and how do we use them? By looking at the diagram below, it is very simple to understand the purpose of these terminals.
Potentiometer pins
The diagram depicts the components found inside a potentiometer. We have a resistive track with a total resistance equal to the POT's rated resistance value.
A potentiometer is nothing more than a resistor with one variable end, as the symbol implies. Assume we have a 10k potentiometer, and we measure the resistance between terminals 1 and 3 and get a value of 10k because both terminals are fixed ends of the potentiometer. Now, as shown above, we can place the wiper exactly at 25% from terminal 1, and if we measure the resistance between 1 and 2, we will get 25% of 10k, which is 2.5K, and measuring across terminals 2 and 3 will give us 7.5K.
We can obtain variable resistance from terminals 1 and 2 or 2 and 3 and the knob can be used to vary the resistance and set the required value.
