Twelve cells each having the same e.m.f are connected in series and are kept to a closed box. Some of the cell are connected in reverse order .The battery is connected in series with an ammeter an external resistance `R` and two cells of the same type as an in the battery .The current when they and support each other is `3` ampere and current is `2` ampare when the two oppose each other. How many cells are connected in servese order ?

Options

A. 4
B. 3
C. 2
D. 1

Answer

D

Explanation

When 'n' cells are reversely connected
`i_(1)=((12-2n)e+2E)/(R)=3" "(i)`
`i_(2)=((12-2n)e+2E)/(R)=2" "(ii)`
From eqns. (1) and (2), `(14E-2nE)/(10E-2nE)=3/2orn=1`