Potentiometer method of DC voltage measurement is more accurate than direct measurement using a voltmeter because
Right Answer is:
It does not load the circuit at all
A null method of measurement is a simple, accurate, and widely used method that depends on an instrument reading being adjusted to read zero current only. The measurement process is to reduce the difference between a known and an unknown quantity to zero, that is, a null would be indicated. The method assumes:
(i) If there is any deflection at all, then some current is flowing;
(ii) If there is no deflection, then no current flows (i.e. a null condition).
The potentiometer method is a null method. At the null point, no current flows in the circuit under measurement. Hence, the potentiometer measures the exact p.d. On the other hand, when a voltmeter is connected to measure p.d. across a component (say a resistor), a part of the current is drawn by the voltmeter. As a result, the current through the component decreases. Hence, p.d. being measured by the voltmeter is slightly less than the actual value.