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

Concept:

Potentiometer:

It is an instrument designed to measure an unknown voltage by comparing it with a known voltage or standard voltage. It is also used for comparing the e.m.f of two cells.

Characteristics of potentiometer:

• As it measures the unknown voltage by comparing it with standard voltage rather than by actual deflection of the pointer. This ensures a high degree of accuracy.
• Potentiometer measures the unknown voltage using null or balance conditions, hence no power is required for the measurement.
• The determination of voltage using a potentiometer is quite independent of the source resistance.

Explanation:

• In the potentiometer, for comparison, the known voltage is used by a standard cell or any other known voltage reference source by using wire.

• It makes use of a balance or null condition, no current flows and hence no power loss is consumed in the circuit
• Measurements by such comparison methods give results of a high degree of accuracy because the result obtained does not depend upon the actual deflection of the pointer.
• As potentiometer measures voltage by comparison.

• The figure shows the symbol of the standard potentiometer.