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Potentiometer is an electric instrument that used to measure the EMF  of a given cell, the internal resistance of a cell. And also it is used to compare EMFs of different cells. It can also use as a variable resistor in most of the applications. These potentiometers are used in huge quantities in the manufacture of electronics equipment that provides a way of adjusting electronic circuits so that the correct outputs are obtained. Although their most obvious use must be for volume controls on radios and other electronic equipment used for audio.

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The principle of the potentiometer is that:

For a wire having uniform area of cross section and uniform composition,the potential drop is directly proportional to the length of wire.

or

The basic working principle of this is based on the fact that the fall of the potential across any portion of the wire is directly proportional to the length of the wire, provided wire has uniform cross-sectional area and the constant current flowing through it.

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