Let polarity of m cells in a 12 cells battery is reversed, then equivalent emf of the battery =(12−2m)E
Now the circuit can be drawn as :When 12-cell battery and 2-cell battery aid each other, then current through the circuit,i1=R(12−2m)E+2E or 3=R(14−2m)E . . . (i)When they oppose each other, the current through the circuit.i2=R(12−2m)E−2Eor 2=R(10−2m)E . . . (ii)Dividing Eq. (i) by (ii), we have23=10−2m14−2mor 30−6m=28−4mor 2m=2∴m=1
