. E LECTRIC C URRENT Imagine a small area held normal to the direction of flow of charges. Both the positive and the negative charges may flow forward and backward across the area. In a given time interval t, let q + be the net amount ( i.e., forward minus backward) of positive charge that flows in the forward direction across the area.
Similarly, let q – be the net amount of negative charge flowing across the area in the forward direction. The net amount of charge flowing across the area in the forward direction in the time interval t, then, is q = q + – q – . This is proportional to t for steady current