In a potentiometer experiment, the balancing length for a cell is 60 cm. When the cell is shunted by a 2Ω resistor, the balancing length becomes 40 cm. The internal resistance of the cell is: MCQ with Answer and Explanation

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In a potentiometer experiment, the balancing length for a cell is 60 cm. When the cell is shunted by a 2Ω resistor, the balancing length becomes 40 cm. The internal resistance of the cell is:

A. 3Ω

B. 4Ω

C. 2Ω

D. 1Ω

Answer: Option D

Solution (By JKExamLibrary)

Potentiometer measures EMF and internal resistance. Formula: r = R(L₁ - L₂)/L₂, where R is shunt resistance, L₁ initial balancing length, L₂ after shunting. Here R=2Ω, L₁=60 cm, L₂=40 cm. Thus r = 2×(60-40)/40 = 2×20/40 = 1Ω. This derives from terminal voltage V = E - Ir and potentiometer principle V ∝ balancing length. Memory tip: 'r = R(L₁/L₂ - 1)'. This advanced numerical tests potentiometer applications, common in competitive exams for experimental physics. Always verify the formula derivation to avoid misapplication.

This question belongs to: Science Physics