In a physics laboratory, the length of the wire of a potentiometer is 1000 mm and it canmeasure upto 2 V.If a standard dry cell of electromotive force 1.5 V obtains a balance at 750 mm, then theelectromotive force for a test cell that obtains a balance at 900 mm will be
Correct answer: A. 1.80 V.
- A. 1.80 V.
- B. 1.25 V.
- C. 0.8 V.
- D. 0.5 V.
Explanation
In a potentiometer, the voltage is directly proportional to the balance length when the current and resistance are constant. Given that a 1.5 V cell balances at 750 mm, the ratio of voltage to length is 1.5 V / 750 mm. For the test cell, the balance length is 900 mm. Using the proportionality: (1.5 V / 750 mm) = (x V / 900 mm), solving for x gives x = (1.5 V * 900 mm) / 750 mm = 1.80 V. Therefore, the correct emf of the test cell is 1.80 V. The other options do not satisfy this proportional relationship.
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