In a potentiometer experiment, the balancing length with a cell is 120 cm. When the cell is shunted by a 1Ω resistance, the balancing length becomes 40 cm. The internal resistance of the cell is :

In a potentiometer experiment, the internal resistance of the cell can be determined using the formula:
L₁/L₂ = r + R/r
where
L₁ is the original balancing length, L₂ is the new balancing length,
r is the internal resistance, and R is the external resistance. Substituting the values, we get
r = 3Ω. Therefore, the internal resistance is 3 Ω. The correct answer is (c) 3 Ω.

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