Potentiometer is an ideal voltmeter as voltmeter draws some current through the circuit while potentiometer needs no current to work. Potentiometer works on the principle of e.m.f comparison. In working conditions, a constant current flows through out the wire of potentiometer using standard cell of e.m.f. `e_(1)`. The wire of potentiometer is made of uniform material and cross sectional area and it has uniform resistance per unit length. the potential gradient, depends upon the current in the wire. A potentiometer with a cell of e.m.f `2 V` and internal resistance `0.4 Omega` is used across the wire `AB`. A standard cadmium cell of e.m.f. `1.02 V` gives a balance point at `66.3 cm` length of wire. The standard cell is the balance point found similarly turns out to be `82.3 cm` length of the wire. The length of potentiometer wire `AB` is `1m`.If the resistance is connected across the cell `e`, the balancing length will be: