Two cells with the same e.m.f. E and different internal resistances r 1 and r 2 are connected in series to an external resistance R . The value of R so that the potential difference across the fir

Question

Two cells with the same e.m.f. E and different internal resistances r 1 ​ and r 2 ​ are connected in series to an external resistance R . The value of R so that the potential difference across the first cell be zero is

TestHub · Accepted Answer

Hints: I = R + r 1 ​ + r 2 ​ 2 E ​ Potential difference across first cell V = E − Ir 1 ​ = 0 ​ E − R + r 1 ​ + r 2 ​ 2 E r 1 ​ ​ = 0 [ R + r 1 ​ + r 2 ​ R + r 1 ​ + r 2 ​ − 2 r 1 ​ ​ ] = 0 ⇒ R + r 2 ​ − r 1 ​ = 0 R = r 1 ​ − r 2 ​ ​

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