Question

20 identical cells each of emf E and internal resistance r are connected in a similar manner in series combination. If terminals of any 2 cells is reversed, then equivalent emf of circuit is

• A. 20E
• B. 18E
• C. 16E
• D. 12E

Answer 1

Answer: (C)

16E

Answer 2

With all cells connected in the same direction, the total emf would be $20E$.

Reversing the terminals of 2 cells makes their emfs oppose the others, contributing $-E$ each.

Thus, the net emf becomes:

$$(18E) + (-E) + (-E) = 16E.$$