The potential energy of the charge at A, by definition, was Q V(A) and
similarly at B, it is Q V(B) Thus, change in its potential energy DUpot is
DUpot = Final potential energy – Initial potential energy
         = DQ[(V (B) – V (A)] = –DQ V
         = –I VDt < 0
(3 28)
If charges moved without collisions through the conductor, their
kinetic energy would also change so that the total energy is unchanged Conservation of total energy would then imply that,
DK =  –DUpot
(3