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  4. Assertion A potentiometer is preferred over that of a voltmeter for measurement of emf of a cell. Reason Potentiometer does not draw any current from the cell.

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Q. Assertion A potentiometer is preferred over that of a voltmeter for measurement of emf of a cell. Reason Potentiometer does not draw any current from the cell.

AIIMSAIIMS 2017

Solution:

When a voltmeter is connected across the two terminals of a cell, it draws a small current from the cell, so it measures terminal potential difference between the two terminals of the cell, which is always less than the emf of the cell on the other hand, when a potentiometer is used for the measurement of emf of cell, it does not draw any current from the cell. Hence, it accurately measures the emf of cell. Thus, a potentiometer is preferred over a voltmeter.