In this chapter, you will begin to learn about alternating current. In contrast to direct current (DC), which flows in one direction at a steady rate, alternating current (AC) sloshes back and forth within a circuit. The primary difference between AC and DC circuits is the source of electromotive force (emf) that is used. Instead of batteries that are used in DC circuits, AC circuits use alternating sources of emf such as AC generators and oscillators. These particular sources of emf keep reversing their polarity over and over, and in doing so, they prod the current to flow back and forth within circuits.