Question 698: Current Electricity

Question

Two cells, having the same e.m.f. are connected in series through an external resistance R. Cells have internal resistances r1 and r2 (r1 > r2) respectively. When the circuit is closed, the potential difference across the first cell is zero. The value of R is

Accepted Answer

KirchhoffÃ¢ÂÂs law has to be applied to the whole loop.
while $$i = {{2E} \over {\left( {{r_1} + {r_2} + R} \right)}}$$
If through one section (here the first battery) has zero potential difference, current cannot flow. The question could have been modified.
The statement that when the circuit is closed, the potential difference across the first cell is zero implies that in a series circuit, one part cannot conduct current which is wrong. KirchhoffÃ¢ÂÂs law is violated.
Assuming that ir
1
= E as given in the question paper, some students could have found that R = r
1
Ã¢ÂÂ r
2
. They have to be given marks.

Answer

r1 + r2

Answer

r1 $$-$$ r2

Answer

$${{{r_1} + {r_2}} \over 2}$$

Answer

$${{{r_1} - {r_2}} \over 2}$$

Current Electricity

Two cells, having the same e.m.f. are connected in series through an external resistance R. Cells have internal resistances r1 and r2 (r1 > r2) respectively. When the circuit is closed, the potential difference across the first cell is zero. The value of R is

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