It is required to measure the true open circuit e.m.f. of a battery. The best device is_____________?
Correct answer: C. D.C. potentiometer
- A. D.C. voltmeter
- B. Ammeter and a known resistance
- C. D.C. potentiometer
- D. None of the above
Explanation
A DC potentiometer measures emf under virtually zero current, so there is no internal-resistance voltage drop and the true open-circuit emf is obtained. A voltmeter draws current and therefore usually reads a slightly lower terminal voltage.
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