Measurement and Instrumentation
For measuring an AC voltage by an AC potentiometer it is desirable that the supply for the potentiometer is taken from

 A battery.
 A source other than the source of unknown voltage.
 The same source as the unknown voltage.
 Any of above.

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Measurement and Instrumentation
Potentiometer method of DC voltage measurement is more accurate than direct measurement using a voltmeter because

 It loads the circuit moderately.
 It loads the circuit to maximum extent.
 It uses centre zero galvanometer instead of voltmeter.
  It does not load the circuit at all.

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