I am writing this week's
experiment in between shows, and
since I am
at FPL's Energy Encounter, I thought we would do an experiment that
involves electricity. It is really a simple one, but it can show us a
lot about how static charges are produced. A few weeks ago, we used a
balloon and some bits of paper to see how humidity had an impact on
static charges. This week, we will look more closely at what was
happening with the balloon and the paper. You will need:
* a balloon. (The cheap, small ones work the best.)
* a piece of paper
First, blow up the balloon and tie it off. Next, take the piece of
paper and tear it up into tiny bits. The pieces should be smaller
than a fingernail. Spread the pieces of paper on the table top. Now,
we want to charge the balloon with static electricity. To do that, we
need to rub the balloon against something. You could use your shirt
sleeve. You could use the carpet. I use my hair (what is left of it).
When two substances come in contact, tiny, negatively charged pieces
of atoms called electrons move back and forth from one to the other.
If one of the objects loses electrons more easily, it will wind up
with fewer electrons and the other will wind up with more. The one
with fewer electrons gets a positive static charge. The one with more
gets a negative static charge. In the case of the balloon and your
hair, the balloon is negative and your hair is positive. Once you get
the balloon charged up, you should be able to get it to stick to your
hair. Opposite charges attract, just as with magnets.
If it won't stick, get out your hair drier. As we learned before,
things need to be very dry for static to work well. After you get
tired of sticking the balloon to your hair, rub it again, to be sure
that it is well charged with static. Then hold it over the pieces of
paper and lower it until something happens. Watch carefully to see
exactly what occurs.
If you lower the balloon slowly, you will notice that the pieces of
paper begin to move. As the balloon gets closer, they fly up and
stick to the balloon. What is going on? We know that opposite charges
attract, but we did not rub the paper against anything. It should not
have any static charge.
Just as opposite charges attract, like charges push away. The
negative charge of the balloon pushes some of the electrons in the
paper away. This leaves a positive charge, which is attracted to the
balloon. Notice that the bits of paper usually do not stick flat
against the balloon. Instead, one end sticks to the balloon and the
other points outwards. When the electrons were pushed away, they were
pushed to the far end of the paper. The end that is stuck to the
balloon is positive and the far end is negative, causing it to repel
the balloon and stick out. Some of the pieces of paper may chain
together, with the positive end of one sticking to the negative end
of the other.
Once the paper touches the balloon, a few electrons from the balloon
can move to the paper. If enough electrons move to the paper, it will
take on a negative charge and will jump away. Once it hits the table,
the whole process starts again.
We produced a static charge on the balloon by rubbing it against
something else. That is the way that most of us think about producing
static charges. Things like walking across a carpet, bouncing on a
trampoline or tumbling the clothes in the drier. With the bits of
paper, we used a method called induction. We brought something that
was already charged with static near them and that charge produced
the charge we wanted.
Induction of static charges is very useful. It can be used to sort
things, such as separating light weight quartz sand from heavier
mineral sands. Static induction also plays a big part in copy
machines, causing the toner to stick to charged portions of the
paper. You can even use it to stick balloons to the wall for a party.
Well, my next audience is coming in, so I will end here. Have fun,
and be sure to clean up all the bits of paper when you are done.
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these
experiments on my web site.
