Principle: The potential drop, across a part of a length l of a uniform wire of length L (L>l), is proportional to the length l.
Two factors:
- Increasing the length L of the wire.
- Connecting a suitable resistance, R, in series with the potentiometer wire.
Reason: At the balance position, there is no net current drawn, from the cell and the cell is effectively in an open circuit condition. This is not so for a voltmeter.