1. The problem statement, all variables and given/known data See the image : http://postimg.org/image/hswmylvz1/ In the image, potential of point a is Va and that of point b is Vb. We have to find out Va-Vb for the circuit as shown in the image. 2. Relevant equations ----- 3. The attempt at a solution Let the potential of negative terminal of the 12 V battery be 0, and its positive terminal's potential be 12 V. Similarly let potential of positive terminal of 24 V battery be 24 V and negative terminal be 0 V. Then potential of a, Va = 0 and potential of b, Vb=0, and so Va-Vb=0, but this is wrong. :( Also, I already got the answer by Kirchoff's loop law, but I wanted to know why above procedure is wrong. Also is the circuit in parallels or in series ? Please help !! Thanks in advance..