By a cell a current of $0.9\, A$ flows through $2\, ohm$ resistor and $0.3\,A$ through $7\, ohm$ resistor. The internal resistance of the cell is ............ $\Omega$
Medium
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(a) $0.9 (2 + r) = 0.3 (7 + r) \Rightarrow 6 + 3r = 7 + r \Rightarrow r = 0.5$ $\Omega$
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