In an experiment to measure the internal resistance of a cell by potentiometer it is found that the balance point is at a length of 2 m when the cell is shunted by a 5 Ω resistance and is at a length 3 m when the cell is shunted by a 10 Ω resistance. The internal resistance of the cell is
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a
1.5 Ω
b
10 Ω
c
15 Ω
d
1 Ω
answer is B.
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Detailed Solution
Let say length without external resistance is l r= ll'−1R ∴ r = l2−1 × 5 →(1) ∴ r = l3−1 × 10 →(2) From eq. (1) and (2) ∴ r = l2−1 × 5 = l3−1 × 10 ⇒l2 −1 = 2l3−2 ⇒ l = 6 m hence , r = l2 −1×5=62 −1×5 =10 Ω
In an experiment to measure the internal resistance of a cell by potentiometer it is found that the balance point is at a length of 2 m when the cell is shunted by a 5 Ω resistance and is at a length 3 m when the cell is shunted by a 10 Ω resistance. The internal resistance of the cell is