Only the slider and one other terminal are used. A potentiometer uses all three terminals, enabling a variable voltage or signal to be tapped off from the slider. Potentiometers and rheostats are made the same way, but rheostats are usually much "beefier", as they are generally used in high-power situations.
What is the principle of a potentiometer?
The principle of the potentiometer is that: For a wire having uniform area of cross section and uniform composition,the potential drop is directly proportional to the length of wire. The above principle is valid when potentiometer is used in comparing the EMF of two cells.
What is driver cell in potentiometer?
Potentiometer is a simple device used to measure the EMF, TPD, internal resistance of a cell. Driving cell (E) of some EMF which is always greater than the EMF (E') to be measured is used to send current through the circuit. It drops uniform potential along the potentiometer wire AB.