Apr 10, 2017

3.5$V$ or 0.5$V$

#### Explanation:

when two cell of potential ${E}_{1}$ and ${E}_{2}$ are connected in series the the net potential adds up to form ${E}_{N e t} = {E}_{1} + {E}_{2}$
similarly for this case when the cells are connected in series the net potential becomes 2 +1.5=3.5$V$
But when we came around the concept of cell getting charged by another cell or there polarity of one of hem is reversed then in that case we the potential cancels out
${E}_{N e t} = {E}_{1} - {E}_{2}$
Here ${E}_{1} > {E}_{2}$
in that case the potential would be 0.5 $V$