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In a potentiometer circuit the wire AB has resistance R0, and cell C (driver) has internal resistance r. The galvanometer G never shows zero deflection for any position of the jockey J on AB. Which of the following can NOT be the reason for this failure to balance?

1. r > R0
2. R >> R0
3. emf of C > emf of D
4. the negative terminal of C is connected to A

Correct answer: emf of C > emf of D

Solution

Balance requires the driver C to produce a larger potential than D's emf with correct polarity; 'emf of C > emf of D' actually enables balance, so it cannot be a reason for no balance.

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