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 4 Ω resistance and at 3 m when ce

Question

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 4 Ω resistance and at 3 m when cell is shunted by a 8 Ω resistance. The internal resistance of cell is

TestHub · Accepted Answer

If ϕ is the potential gradient then, V A - V B = ϕ × l when the cell is shunted by a 4 Ω resistance, E - E r r + 4 = ϕ × 2 E 4 r + 4 = ϕ × 2 ........ (1) Similarly, when the cell is shunted by a 8 Ω resistance, E 8 r + 8 = ϕ × 3 ......... (2) From equation (1) and (2), r + 8 2 r + 4 = 2 3 3 r + 24 = 4 r + 16 r = 8 Ω

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