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Alternating Current — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current3 Marks
Question
State the underlying principle of a potentiometer. Write two factors by which current sensitivity of a potentiometer can be increased. Why is a potentiometer preferred over a voltmeter for measuring the emf of a cell?
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Answer

Principle: The potential drop, across a part of a length l of a uniform wire of length L (L>l), is proportional to the length l.
Two factors:
  1. Increasing the length L of the wire.
  2. Connecting a suitable resistance, R, in series with the potentiometer wire.
Reason: At the balance position, there is no net current drawn, from the cell and the cell is effectively in an open circuit condition. This is not so for a voltmeter.

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