This Week's Experiment - #308 Static Glow
The cold weather has made the static electricity much better (or worse,
depending on how you look at it). While the humidity of living at the beach
usually makes our lives fairly static free, our dog and cat are discovering
that in this weather, almost any touch can involve a spark. With all of that
static, I thought that I should use it for this week's experiment. To have
some fun with static, you will need:
a fluorescent bulb
a balloon
a dark room
First, be very careful with the fluorescent bulb. They break easily and
contain mercury, so if young children (or clumsy adults) will be using them,
go to the hardware store and get one of the cheap, plastic covers that fit
over the bulb. That will make it safe and easy to clean up if the bulb
breaks.
Blow up the balloon and tie it off. Rub it on your hair and see if it will
stick to the side of your head. If it sticks, then you are getting plenty of
static. If it does not, then you probably have too much humidity (or too
little hair, like me). Dry the balloon and your hair with a hair drier and
try it again. You can also try someone else's hair.
Once you are getting plenty of static, go into the dark room. Hold the
balloon in one hand and the fluorescent bulb in the other. Have someone turn
out the lights and then stand there until your eyes get used to the dark. Be
sure that the room is very dark, even when your eyes adjust. Even a little
light coming under a door can make it difficult to see the results.
Now comes a challenge to your coordination. In the total darkness, you are
going to rub the balloon on your hair. Then touch the balloon to the side of
the fluorescent bulb. If the room is very dark, and if you are getting
plenty of static and if your eyes are adjusted to the darkness, and if you
can find the fluorescent bulb in the dark, you should be rewarded with a nice
flash of light. It will not be a bright flash, but it should be enough to
see.
How can the balloon produce enough electricity to light the fluorescent bulb?
To answer that, we need to know a little about how light bulbs works. A
regular, incandescent bulb lights by using the electricity to heat a wire
filament inside the bulb. When this filament is hot enough, it begins to
glow and you get light. Incandescent bulbs need a lot of amperage. Amperage
tells us how much electricity. They do not need much voltage, which is how
hard we are "pushing" the electricity through the wires. The electricity you
are generating with the balloon is just the opposite. It has a very small
amperage and very high voltage. You would not be able to light an
incandescent bulb with it.
A fluorescent bulb does not produce its light with a wire. Instead it uses a
gas. Most of the air has been removed from the tube. It has been replaced
by a tiny amount of mercury vapor, at low pressure. When high voltage
electricity forces it way through the gas in the tube, the gas is changed
into plasma (the fourth state of matter). Plasma is like a gas, but some of
the electrons have been ripped from the atoms. The plasma is a good
conductor of electricity. It also gives off light. Unfortunately, the light
this plasma gives off is ultraviolet, sometimes called black light. It is a
color that our eyes cannot see. Luckily, the white powder on the inside of
the glass tube glows under ultraviolet light, and we can see the light from
that glowing powder. Forming the plasma in the fluorescent bulb requires
high voltage, but does not need much amperage. That is exactly what we are
producing with the balloon, so it can light the bulb.
You don't need to have the balloon to light the bulb. Anything that produces
a good static charge will do it. Try taking a load of clothes, fresh from
the drier, into the room. Touch the bulb with the socks as you pull them
from the other clothes. In the dark room, you will notice tiny sparks as you
pull the socks away from the other clothes. You see those sparks because the
electricity is changing the air around you into plasma. The air you breathe
is mostly nitrogen, which glows purple when the spark changes it to plasma.
When you touch the socks to the bulb, you should see a faint, white flash as
the mercury vapor is also changed to plasma.
Feel free to try other sources of static, but stick with static. Do not try
to use the electricity from a wall socket. It would not work, because it is
too low voltage. The fluorescent lamp steps up the voltage so that it can
light the bulb. It would also be very dangerous because household current can
kill. Be safe and have fun. And fold the laundry when you are done. Have a
good week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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