In the circuit shown below, let v₁ be the voltage across R₁ and v₂ the voltage across R₂.

It is clear that in a circuit such as this one, the voltage of the supply is divided up in the same ratio as the ratio of the resistances.

For this reason, circuits of this type are often called potential dividers.

A variable potential divider can be made using all three connections of a variable resistor. (A variable resistor can also be called a rheostat.)

Variable Resistors

i) Rotating variable resistor (internal view)

ii) Linear variable resistor