Vicky Ratliff, age 12, of Jemison, Alabama, for her question:

What is meant by AC and DC?

In both cases the C stands for current, the electric current carried from here to there in a wire circuit. Its power is created and started on its round trip by mighty electric generators. Their whirling turbines push voltage through the wires by spinning copper coils through magnetic fields. This pushes teeming streams of moving electrons through the circuit. The direction in which the electrons move is determined by the power plant.

When all the electrons move in the same direction, they create direct current    DC. When they jog back and forth, they create alternating current    AC. For example, in a 60 cycle AC current, the electrons in the wires jog back and forth 60 times per second. Most of our generators create AC current because we can send it long distances. Giant pylons carry power of maybe 230,000 volts. Transformers are needed to step down such mighty power for general use. And transformers can step down alternating current, but not direct current.