When an external resistance of 5 is connected across terminals of a cell, a current of 0.25 A flows through it. When the 5 resistor is replaced by a 2 resistor, a current of 0.5 A flows through it. The internal resistance of the cell is .
1
Using E = I(R + r) for the two cases:
E = 0.25(5 + r) and E = 0.5(2 + r)
0.25(5 + r) = 0.5(2 + r)
1.25 + 0.25r = 1 + 0.5r 0.25r = 0.25
r = 1 (and E = 1.5 V)
Answer: 1
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