For this week's experiment, we are going to watch our fingers wiggle. Doesn't that sound like fun? OK, I admit that I am easily amused, but there is more to this experiment than just moving your finger. We are going to investigate part of how a television works at the same time.

For this experiment, you will need:

- a television or computer monitor (not plasma or LCD)
- a lamp or other light source
- your fingers

Turn on the lamp and hold your hand between your face and the lamp. Stick up your first finger and wave it back and forth. Observe carefully how your finger looks as it moves from side to side. Yes, you are right. There is still nothing different or surprising going on. Don't give up. It gets better.

Now, turn on the TV. See, I told you it would get better. Hold up your finger in front of the TV screen and wave it from side to side. Do you notice any difference? You should. Instead of seeing your finger move smoothly from side to side, you will see a series of separate fingers, side by side. I know that sounds strange, but try it and you will see that even though it is hard to describe, it is easy to see.

Why does the television do that? When you move your finger in front of a light bulb, the light is always on, so you see wide blur of your finger moving from side to side. Your television is not on all the time. It is flickering on and off, very quickly. Moving your finger in front of the television causes your finger to be lighted by the screen each time the screen lights up. In between, the light is off and your finger does not show up.

In the US, televisions flicker on and off 30 (actually 29.97) times each second. In Europe, they flicker 25 times per second. This flickering is due to the fact that your TV screen is made up of lots of tiny dots called phosphors. These dots light up one at a time. The first one lights up and is turned off. Then the second one, and then the third, and so on. In one second, your television can light up each phosphor 30 times. Your brain puts all of the dots together and forms the moving pictures on your TV.