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Krampf #471 Street Lights
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KRA-@aol.com
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Dec 13, 2006 22:45 PST
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Robert Krampf's Experiment of the Week
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I am sending this experiment again, since many of you seem not to have
recieved it.
This Week's Experiment - #471 Street Lights
Greetings from Miami. Nancy and I had a wonderful Thanksgiving in Memphis,
TN with my family. Looking back over my life, I have so much to be thankful
for. I have a wonderful family, and an incredible wife. I have been
blessed with marvelous friends (and I include all of you as friends). I have more
fun with my job than most people do when they are playing, and it has lead me
on many adventures, from digging dinosaur bones to mapping caves, from petting
Gray Whales in Mexico to holding million volt sparks in my hand. What a
wonderful life!
I ate enough turkey and dressing to keep me going for quite a while, so no
ice cream experiments this week. Instead, the experiment comes from our
flight. We flew at night, and as I was looking out the window, I noticed that the
streetlights were different colors. Some were bluish white, and others were
yellow. The more I looked; the more I wanted to know why there were two
different colors. To explore the differences, you will need:
a blank CD or DVD
streetlights
A bit of research showed that there are several kinds of street lights, all
grouped under the name High Intensity Discharge Lamps. They all work in
basically the same way. A high voltage spark jumps through a gas, such as mercury
vapor or sodium vapor. This changes the gas into plasma, a different state
of matter. Plasmas give off light. Common examples of plasma include neon
signs, fluorescent lights, lightning and stars, including our Sun.
Different substances glow different colors when they are changed to plasma.
The bright orange of the OPEN signs that many stores use is the color of neon
plasma. Argon plasma glows blue. Sodium plasma produces the yellowish
color that you see in street lights.
With mercury vapor, we have to take things one more step. When changed to
plasma, mercury vapor gives off light that has a lot of purple and ultraviolet.
Ultraviolet, sometimes called black light, is a color that our eyes can't
see. It is the part of the spectrum that gives you a sunburn. It can also
make some objects glow, as they absorb the ultraviolet and give it back as a
color that our eyes can see. That is what is happening inside the mercury
vapor lamps. It is also what happens in a common fluorescent tube, which
explains why those tubes make such a mess if they break. The inside of the glass is
covered with a white powder that absorbs the ultraviolet light and glows with
a blue-white light.
While the colors of the streetlights are easy to see, once you really look at
them, there is an even bigger difference if you use a CD or DVD. You have
probably noticed that you see rainbow colors when the light reflects off a CD.
Try the same thing with a streetlight, and you will see something
interesting. Instead of a long, thin, even rainbow, the light from the streetlights
will produce rainbows that have thick "beads" for the colors that make up most
of the light, and dark spots for colors that are missing. If you compare this
spectrum for the different street lights, you will see very different
patterns.
This is a very useful thing. Different plasmas give off different colors.
Have you ever wondered how we know that the Sun is made up mostly of hydrogen
and helium? No one has scooped up a bit of it to analyze, but we can use
the light that it gives us to see what it is made of. These "rainbows with
holes and bright spots" can also be used to identify chemicals here on Earth.
Burning a substance and examining the light spectrum it gives off will tell us
what the substance is made of. I wonder if I could use that to figure out
the exact recipe that my Grandmother uses to make the gravy for her pot roast!
Yum!
Have a wonder filled week!
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Robert Krampf's on-the-road schedule:
My calendar is now on-line. You can see a detailed calendar, with dates,
times, schools, etc. at http://www.krampf.com/m_tour.html
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Check out my web site at:
http://www.krampf.com
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
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