Most people have heard of AC and DC, but sometimes it is hard to grasp the difference. DC or direct current is electricity that always flows in the same direction. A good example of this is the electricity that comes from a battery. On the other hand, the electricity that we get from the outlets in your home is alternating current or AC. This alternating current goes through the wires in one direction, then stops and flows in the opposite direction. In the U.S., our electricity alternates back and forth 60 times each second. In some other countries it goes back and forth 50 times each second. Either way, you can actually see that it is alternating. You will need:

- Several appliances that have an orange or red indicator light to show when they are turned on.

You may have to try several different appliances to find one that works. Coffee pots are usually good. So are the power strips that let you plug several things in at once. If you have one of the new extension cords that has an indicator light built in, they are wonderful for this experiment.

Turn on the appliance. First, check with an adult, to be sure that you don't mess up the appliance. Turning on a coffee pot without adding water can cause all sorts of problems. Now, stand a few feet away and look at the indicator light. Shake your head back and forth. If you have the right appliance, you should see that the light is flickering on and off very quickly. It happens so fast that you will not see it when you hold your head still. If it does not flicker, try a different appliance. An easy way to do this is to wait until night and then turn out the lights. If your house is like mine, there are lots of little glowing lights on all of the electrical things. Then just shake your head and watch for the flicker.

The indicator lights in many of these appliance are actually small neon bulbs. They use neon because it does not need a filament and won't burn out. Since neon gives off orange light, you want to look for orange or red indicator lights. A regular bulb lights up because inside the bulb, a thin wire called a filament gets very hot and glows. When the alternating current turns off for a fraction of a second, the filament does not cool off enough to stop glowing. That is why you cannot see the flicker with this kind of bulb.

A neon bulb glows because the electricity changes the neon gas into plasma. (The fourth state of matter.) As soon as the electricity stops, the plasma changes back into a gas and stops glowing. With a neon light, it is easy to see the flicker caused by alternating current.

Some appliances use LEDs (Light emitting diodes) as indicator lights. These may flicker or not, depending on the type of electricity (AC or DC) that they are powered by. LEDs can be red, green, yellow or other colors. Be aware that many AC appliances convert the electricity to DC, which means their LED may not flicker, even if they are plugged into a wall outlet.

If you look at enough appliances, you should be able to find at least one that flickers. I even noticed that the red lights on our local radio towers flicker, showing that they are powered by alternating current.