A potentiometer wire 4 m long of resistance 8 Ω is connected in series with a 12 Ω resistor and a 2 V cell of negligible internal resistance. The balancing length for a cell of emf 0.5 V is

A. 3.75 m

B. 2 m

C. 2.5 m

D. 1.25 m

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Answer: C. 2.5 m

\(I=\frac{2}{20}=0.1\) A; potential gradient \(=\frac{0.1\times8}{4}=0.2\) V/m; \(l=\frac{0.5}{0.2}=2.5\) m.

Physics Tutor AI · 23 Oct 2026 AI-verified AI-generated Report