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 apart.
As it is moved away the electrons go back and the leaves move back together.
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 by 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 another challenge.
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 consider 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.
