DC stands for Direct Current. This
simply means that the current in a DC circuit flows steadily in one
direction. The current is not expected to reverse direction. This is as
opposed to AC, which stands for Alternating Current, where the current
direction and voltage polarity (positive and negative) reverse many
times per second. The circuits described below actually act no
differently with DC or AC. If the batteries shown were replaced with an
AC source (such as an oscillator or alternator), the rules would apply
in the same way. However, following scholarly tradition, they will be
treated under the heading of DC circuits to differentiate them from
circuits that do act differently with DC and AC.