Five cells each of emf E and internal resistance r send the same amount of current through an external resistance R whether the cells are connected in parallel or in series. Then the ratio ((R)/(r)) is

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Correct answer: D. 1

Given : Number of cells, n=5 , emf of each cell =E Internal resistance of each cell =r In series, current through resistance RI=(n E)/(n r+R)=(5 E)/(5 r+R) In parallel, current through resistance RI^ =(E)/((r)/(n)+R)=(n E)/(r+n R)=(5 E)/(r+5 R) According to question, I=I^ (5 E)/(5 r+5 R)=(5 E)/(r+5 R) 5 r+R=r+5 R or R=r (R)/(r)=1

Five cells each of emf E and internal resistance r send the same...

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