Q193 / 200 · MHT CET - Medical 2026 (23 April Shift 1) · Physics

In a potentiometer experiment, the balancing with a cell is at length $240$ cm. On shunting the cell with a resistance of $2\ \Omega$, the balancing length becomes $120$ cm. The internal resistance of the cell is

  • A
    $1\ \Omega$
  • B
    $0.5\ \Omega$
  • C
    $4\ \Omega$
  • Correct answer
    D
    $2\ \Omega$

Solution

The internal resistance $r$ of a cell determined using a potentiometer is given by the formula:

$r = R \left( \dfrac{l_1}{l_2} - 1 \right)$

Given $l_1 = 240$ cm, $l_2 = 120$ cm, and $R = 2\ \Omega$.

Substituting the values:

$r = 2 \left( \dfrac{240}{120} - 1 \right)$

$r = 2 (2 - 1)$

$r = 2\ \Omega$

Answer: $2\ \Omega$

Hence, the correct answer is option: 'D'.

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