Question

27. Two cells, each of emf 1.5 V are joined in series and
send 1.0 A current in an external resistor. If the same
cells are joined in parallel, then they send 0.6 A
current in the same resistor. What is the internal
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Answer 1

Answer:

Explanation:

connecting 2 cells in series adds up the emf, thus 3V = 1(R+2r) (‘R’ is the external resistor and ‘r’ is the internal resistance). Now, the same cells are again connected in parallel, this makes the potential same thus, it remains to be 1.5 V, therefore, 1.5V = 0.6 (R + r/2). On solving you get r = 1/3