VocExile Main Menu /Electroscope
By Ed Perley
An electroscope is a device that is used to demonstrate properties of static electricty. Static electricity is a phenomenom that takes many forms. It can be an electric shock you can get after walking over a carpet, or it can be a lightning bolt from the sky. The electroscope demonstrates the repulsive force that is exerted between two nearby objects with the same electric charge. This page tells how you can make your own electroscope from materials commonly found in your house.
The design of this device was described in the Omaha World Herald's "This Week Magazine" in the late 1950,s, a time when the fear of nuclear war and the resulting nuclear radiation was very real. It was billed as a simple device for detecting dangerous levels of this radiation. But it is also useful for demonstrating repulsive forces associated with static electrity.
Run a plastic comb through your hair and touch it to the circles. After a moment of attraction they will repel each other. The static electricity will hold them about an inch apart.
Carefully hang the circles in the jar, trying to keep them from touching the aluminum foil liner. If necessary, a quick touch of one of the circles with the inside wall will reduce the gap between them, making this action easier.
Rubbing a comb in your hair puts a positive charge on the comb. Touching the comb to the circles transfers some of the charge to them. Because of their light weight, static electric repulsive forces push them apart.
The foil lined jar serves as an electrostatic "bottle" that slows the rate at which the charge leaks away. This loss of charge will happen more rapidly in a location where there is nuclear radiation. Impacts of beta rays, high energy negatively charged electrons, will cause the circles to lose their positive charges. Therefore the gap between the circles will close more rapidly.
This device can be used to detect dangerous levels of beta radiation. It will not detect other forms of nuclear radiation. Alpha particles are positively charged, but they are too massive to penetrate the glass. Gamma rays and neutrons can hit the circles, but because they have no charge, they have no significant effect.
I recently discovered I still have the instructions for calculating radiation levels using the electroscope. There will be a possibility of error because I do not remember for sure the spacing between the line on the scale. (I think it is 1/8 inch, but it could be 1/16 inch.)
Multiply the number of seconds for the leaves to go together from one pair of scale lines to the next, by ten. The value you get is the number of hours of exposure you can survive at the current radiation level. A time of 600 seconds (10 minutes) indicates no significant radiation. Under normal conditions, it should take between ten and thirty minutes for the leaves to move from one pair of scale lines to the next.
You may have some potential low level radiation sources to test with your electroscope. Color televisions, especially the oldest ones, emit radiation, mostly from the top and sides. Smoke detectors, may also give off some radiation. If you have access to radioctive isotopes in a nuclear lab, you could put it inside the jar for maximum effect. (Don't have anything to do with nuclear isotopes unless you know what you are doing!) I have never done any experiments like this. Please let me know if one works for you. Forget about microwave ovens. Their radiation is much different.
So, have fun experimenting with your electroscope. And, if there ever is (heaven forbid) a nuclear holocaust or nuclear reactor meltdown, you'll be ready.
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