This is a very sound stupid question, but I'll go ahead anyway. Current is defined as the displacement of charge through a cross-section of a conductor per unit time. Okay. But how does relate to its math-definition, current = change of charge with respect to time, I=dQ/dt? I mean, for every charge leaving the cross-section of the conductor, an equivalent one will enter. This means that across the cross-section dQ/dt, the summed change of charge with respect to time, equals 0! I find I = Q/t, current = amount of charge passing the cross-section per unit time, a much more intuitive definition.. So can you guys help me make sense of this?