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Bouncing Remotes

This experiment comes from spending too much time in hotel rooms as I travel. As I was packing for the trip home, I found a very useful technique for adjusting the television when I was not directly in front of it.

For this experiment, you will need:

  • a television, VCR or some other device operated by a remote control
  • a remote control
  • a mirror

How does the remote on your television work? You just push a button and it changes the channels. Is it magic? No, of course not. Many people think it is a radio control. Lets find out. First, sit in your favorite place to watch TV. Use the remote to turn the TV on. Now change the channel. Everything works just fine.

Now point the remote control towards the floor and try changing channels. Does it work? Probably not. Try pointing the remote in different directions to see what works. You will soon find that you usually need to point the remote directly towards the TV for it to work, but you may find other directions that work very well. Why is this? If the remote was using a simple radio signal, then the direction would not matter. If it was a directional radio beam, then it would only work when it was pointed towards the TV.

Place the mirror on a chair so that it is facing the TV. Sit on the floor with your back to the TV. Point the remote towards the mirror and try changing the channels. It works! If it does not, try shifting the mirror until it does. Be sure you are not sitting between the mirror and the TV.

This shows us that the signal from the remote is bouncing off of the mirror to the TV. What bounces off of a mirror? Light! But if it was light, wouldn't we be able to see it? Even in a dark room, you cannot see any light coming from the remote.

What is happening? The remote control uses a color of light that we cannot see. It is called infrared light. Just as there are sounds that we cannot hear, such as "silent" dog whistles, there are colors that we cannot see. The remote is flashing patterns of infrared light to the TV, where a sensor picks it up and changes the channel. Because it is light, it will reflect off of a shiny surface. This can be a mirror, the glass of a picture frame, or anything else that is shiny. Try arranging two or more mirrors or picture frames so that you can bounce the beam and turn change the channels from another room. The beam spreads and weakens with distance, so don't expect to be able to get too many bounces.

Science Fair Thoughts:

Are there filters which you can see through, but that will block the IR beam of the remote control? Are there filters that block your vision, but let the IR beam get through? Can you use a lens to focus the IR beam? How much does the IR beam spread over a set distance?