Charging an Ipod with Direct Current Source(Batteries).
Till now we have explored the basic physics of direct current. This is the type of electricity that is produced by batteries, by rubbing certain types of materials against each other, lightning etc. A voltage is created, and possibly stored, until a circuit is completed. When the circuit is complete, the current flows directly, in one direction at a specific, constant voltage. When we use a flashlight, pocket radio, portable CD player, Ipod or virtually any other type of portable or battery–powered device, we are using the direct current. Most DC circuits are relatively low in voltage.
But most present day household and industrial power distribution systems operate with alternating current. Alternating current is a current that varies continuously in magnitude and periodically reverses its direction. The electricity is not provided as a single, constant voltage, but rather as a sinusoidal (sine) wave that over time starts at zero, increases to a maximum value, then decreases to a minimum value, and repeats. A representation of an alternating current's voltage over time is shown in the diagram. Any appliance that we plug into a wall outlet uses alternating current. Circuits in modern communication equipment, including computers and televisions make use of alternating currents (AC) extensively.