The difference between AC and DC is that AC is an alternating current (the amount of electrons) that flows in both directions and DC is direct current that flows in only one direction; the product that is flowing being electrons. AC power is what fuels our homes. The wires outside of our house are connected at two ends to AC generators. DC is found in batteries and solar cells. Both AC and DC employ magnets to repel electrons. Electrons are negatively charged particles that are one of 3 components that make up an atom. Negative charges will repel negative charges and positive charges will repel positive charges, so one only needs to introduce a negatively charged item next to electrons to force them to move in the opposite direction. Likewise, you can attract electrons by introducing something that is positively charged into their environment drawing the electrons to it. This property of electrons is what allows for AC power to work; that is, they switch directions constantly. The picture to the left is a demonstration of AC power at work. The constant switching of directions is evident in the dotted appearance of the light lines.
DC power was invented by Thomas Edison and first used to power our homes in the late 1800′s. Its main drawback being that in order to receive DC power from a generating station, your home had to be located within a one mile radius of the station. DC power degrades as it moves away from its generating source; the further away, the less power. In addition, it is difficult to convert very high power DC current into the lower power current needed in our homes.
Nikola Tesla discovered AC and sold his design to Westinghouse. AC power degrades very little over 100′s of kilometers. When the power reaches an electrical pole outside our homes, a transformer converts to high voltage (the amount of energy carried with the electrons) to the low voltage needed to fuel our appliances. To convert AC to DC, a device needs an item called a rectifier. Many monorail systems use DC power. In addition, if you have a portable stereo, you may notice a button on the back that can switch from AC to DC; this means that you can power your device by plugging it in (AC) or by using batteries (DC).