A potential divider a voltage and reduces it to another voltage. It does this using a series circuit in which the voltage across each resistor is divided in the ratio of their resistances.

The total resistance in the circuit above issince these resistances are in series. Then

Now applyto

The power dissipated byis maximum when

A potentiometer has the same arrangement, with the difference that the resistances are continuously variable. One such is shown below.

By moving the point of contact A, the ratio x:y and R_1 : R_2 can be changed continously. Equation (1) becomes