The best instrument for the accurate measurement of the e.m.f. of a cell is

Options

A. Potentiometer
B. Metre bridge
C. Voltmeter
D. Ammeter and voltmeter

Answer

A

Explanation

We know that E = I(R + ) which means E = V + Ir where, V = IR
To measure emf of a cell (V = E) we need to either make internal resistance (i) equal zero. which is not possible, or make current() equal to zero. A potentiometer is the only instrument which can be set up in such a way that no current is drawn from the cell. Every other instrument always draws some amount of current which doesn.t allow the proper measurement of emf.