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Electricity and Magnetism
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.)
i) Rotating variable resistor (internal view)
ii) Linear variable resistor