WBCS Preliminary Examination 2021 — General Studies · Question 88 of 200

Answer: (C) 6V

In a series battery, each wrongly (reverse) connected cell not only fails to add its emf but also cancels one correctly connected cell. With $n$ cells of emf $E$ and $m$ of them reversed, net emf $=(n-2m)E=(10-2\times2)\times1=6\,V$ - equivalently, 8 cells aid ($8\,V$) and 2 oppose ($2\,V$). Option (A), $8\,V$, is the common mistake of merely leaving out the two cells. The internal resistances of all 10 cells still add up, so the current falls even further.