It is a device to measure the potential difference across a circuit element accurately. The circuit containing battery B1 is the main circuit and the circuit containing battery B2 is the secondary circuit. For the working of potentiometer emf of battery B1 > emf of battery B2. When a steady current is passed through a potentiometer wire AB, there is a fall of potential along the wire from A to B. The fall of potential per unit length along potentiometer wire is called the potential gradient. If L is length of wire AB and V is the potential difference across it then
Potential gradient k = V/L
The S.I. unit of potential gradient is volt/metre.
