Wire A and B, which have the same cross-sectional area are connected in series. There is a p.d. V across the whole wire. Suppose the two wires obey Ohm's law J = σE Also, A and B have different conductivity. Therefore electric field of A is different from B. There should be a layer of charge between the junction of A and B. So, when does the charge accumulation start ? At the transient time ? At that moment, current flows in wire A =/= current flows in wire B ?