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MHT CET202519 Apr 2025Evening ShiftPhysicsCurrent ElectricityActual

To determine the internal resistance of a cell with potentiometer, when the cell is shunted by a resistance of 5 , the balancing length is 250 cm . When the cell is shunted by 20 , the balancing length of potentiometer wire is 400 cm . The internal resistance of the cell is

Options

  1. A3
  2. B4
  3. C5
  4. D6

Correct answer

C. 5

Step-by-step solution

The internal resistance r of a cell using a potentiometer is determined by the formula r = R ( L₀ L - 1 ) , where R is the external shunt resistance, L₀ is the balancing length for the cell's EMF in open circuit, and L is the balancing length for the terminal potential difference. Given two cases: with R₁ = 5 , and L₁ = 250 , cm , and R₂ = 20 , and L₂ = 400 , cm , the expressions for internal resistance are: r = 5 ( L₀ 250 - 1 ) r = 20 ( L₀ 400 - 1 ) Equating the two expressions: 5 ( L₀ 250 - 1 ) = 20 ( L₀ 400 - 1

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