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Question
It is observed in a potentiometer experiment that no current passes through the galvanometer when the terminals of the cell are connected across a certain length of the potentiometer wire. On shunting the cell by a 2 Ω resistance, the balancing length is reduced to half. The internal resistance of the cell is ______.
Options
2 Ω
18 Ω
9 Ω
4 Ω
Solution
It is observed in a potentiometer experiment that no current passes through the galvanometer, when the terminals of the cell are connected across a certain length of the potentiometer wire. On shunting the cell by a 2 Ω resistance, the balancing length is reduced to half. The internal resistance of the cell is 2 Ω.
Explanation:
The internal resistance of the cell is given by:
r = `("I"_1/"I"_2 - 1) xx "R"`
r = `((2"I"_1)/"I"_1 - 1) xx "R"`
`=> "r" = (2 - 1) xx "R"`
r = R = 2Ω
