A potentiometer is an ideal voltmeter since a voltmeter draws some current through the circuit while potentiometer needs no current to work. A potentiometer works on the principle of emf comparison. In working condition, a constant currant flows throughout the wire of a 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 emf `2 V` and internal resistance `0.4 Omega` is used across the wire `AB`. A standard cadmium cell of emf `1.02 V` gives a balance point at `66 cm` length of wire. The standard cell is then replaced by a cell of unknows emf `e` (internal resistance `r`), and the balance. Point found similarly turns out to be `88 cm` length of the wire. The length of potentiometer wire `AB` is `1 m`. The value of `e` isA. `1.36 V`B. `2.63 V`C. `1.83 V`D. `none