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Invisible Light
I try to find experiments that use things that most people will
have around the house. I thought about this week's experiment for quite a while
because it uses a video camera. If you do not have a video camera, you can still
do this one by going to a department store that sells video cameras. They
usually have several cameras set up for people to try. You will need:
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a video camera
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a remote control
A remote control is one of those amazing devices that are so
common that we tend to take them for granted. We have shown in past experiments
that the remote control uses an invisible beam of light by bouncing it off
mirrors to control the television. This week, we will actually see the invisible
light.
Now wait a minute. How can light be invisible? Well, just as
there are sounds that our ears can't hear, there are colors that our eyes can't
see. Imagine a rainbow. The colors are in order, from red at one end to
violet at the other. There are also colors on both sides that our eyes can't
see. Just past the violet, there is ultraviolet or UV light. This is
commonly known as black light, not because it is black, but because our
eyes can't see it.
Just beyond the red is another color we can't see, infrared.
That is the color that we are interested in today. Lets try to see some infrared
light. Get the television remote. Look into the end of it and press a
button. Did you see any flashes of light coming from the end? No. Some
remotes have a small red light on them too, to let you know that the remote is
working, but the light we are interested in comes from the dark plastic at the
front end of the remote.
Maybe is it just too dim to see. Try going into a very dark
room. Let your eyes adjust to the darkness and then watch again as you press the
buttons. Still nothing we can see. Your eyes just can't see infrared light, no
matter how dark the room is, and no matter how bright the infrared light is.
Now for the fun part. Turn on the video camera and look through
the viewfinder. Point the remote into the camera and press a button. You see
bright flashes of light! How can the video camera let you see something that is
invisible?
While our eyes can't see infrared light, a video camera can
detect it. The sensors that pick up the image in the camera are sensitive to a
wider range of colors than our eyes are. Luckily, your camera is not built to
display infrared light. Instead, it shows up as visible light, letting you see
the flashes.
Press different buttons on the remote as you watch through the
camera. They will all look pretty much the same. How can that work? Just as the
camera can pick up colors that your eyes can't see, the receiver on the
television can detect flashes that are too fast for your eyes to catch. What
looks like a single flash to you is actually a very fast series of flashes. Each
button on the remote produces a different pattern of these flashes, sending a
different command to the television.
So this week, as you sit on the sofa and use the remote, think
about those days in the distant past when we actually had to walk across the
room to change the channel, and all of the science that is involved in saving
you that trip.
Have a wonder filled week.
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