of our 6th graders
favorite classes is when they take a look at static electricity and
what it can do and what it feels like.
A simple electroscope that Ben Franklin would recognize.
The balloon has been negatively charged by rubbing it on someone's hair.
When it is moved close to the knob of the electroscope that charge
repels some electrons to the metal foil leaves causing them to move
As it is moved away the electrons go back and the leaves move back
If it is charged and someone touches it the electrons will have a path
to ground and the leaves will come back together.
A small cheerleader pompom shows the same effect when it is charged by
a Van de Graaff.
Then we used it to charge some students so they could demonstrate with their hair as the electroscope.
Nancy tried it too.
A stack of aluminums pans on top of the Van de Graaff is repelled one
The challenge is to catch them in the big pan
It isn't easy. They come fast.
She just caught one and there is another in the air with more to come.
The "wand" has 13 Xenon flash tubes in series each requiring about 1000
volts each to conduct.
The charge goes into the student's hand as it is on its way to ground
and he is shocked each time they flash.
Here the students are making a chain
with fluorescent bulbs between each of them.
The first student will use the pan to make contact with the Van de
Graaff to supply the current for the next demonstration.
Is everyone ready?
When a spark jumps they all feel it.
Then we turn out the lights so they can see the bulbs light up as the
current goes through the bulbs.to the next person in line.
Next they could take on the full charge one on one.
Anticipation was almost worse than the spark.
I said almost!
One of the teachers tested her nerve too.
A string made of alternating conductive and insulating beads was
Initially the students held on to the end of the string.
The voltage wasn't great enough to jump all the insulating gaps but as
they slid their hand closer to the Van de Graaff it would flash between
the beads to them.
This video shows it even better.
We also had a set of
Franklin's Bells. Here the bell closest to the Van de
Graaff is charged without any
contact with the terminal. Corona discharge from the sharp edges
of the aluminum foil to the
terminal is all it takes. The bell attracts the blue bob which
swings toward it. As soon as it makes contact the bell
and bob have the same charge so
the bob is repelled and swings toward the other bell. When it touches it shares its charge
with that bell and now both of
them have the same charge so the bob is repelled from there. The bob having lost much of it's
charge it can be attracted to the
first bell again and the process repeats. Even after the Van de Graaff is
turned off the process continues. Its terminal is still at high voltage
until the charge leaks away.
Another device you may
unlikely. It is a motor made from some pop
bottles and aluminum foil and powered
by electricity traveling through the air. Construction is simple, bottle (1) on
one end is charged by corona
discharge from a piece of aluminum foil attached to it and pointed
toward the Van de Graaff. The bottle (3) on the other end
discharges current that reaches it
through a similar bit of foil pointed away. Between them is another bottle (2)
that is free to turn and has
vertical stripes of foil on it. The stripes are charged by corona
from yet another foil electrode
attached to bottle 1. The stripe takes on the same charge
and so is repelled and moves away,
another takes its place, and the process repeats. Charge is removed from the stripes at
the other end by another piece of
foil attached to bottle 3. To be clear, none of the aluminum
foil electrodes touch anything other
than the air and yet there is enough power for the motor to spin nicely.
Great fun for all.