My Electroscope

A sensitive electroscope is essential when experimenting with static electricity. This temporary construction is the product of giving it some thought as to how to make my own electroscope. It works well (up to about 50% relative humidity, at which point it starts to disharge), is quite sensitive and gives reproducable results. I intend to mount it permanently at a later stage. It also quantifies the amount to which an object is electrified and gives large deflections which can easily be viewed from a distance. Maybe I should should rather call it an electrometer due to this feature.

The components are mounted on a 25 millimeter thick sheet of polystyrene about 100 centimeters high by 42 centimeters wide. Two small blocks of polystyrene are glued down at the top of the sheet. A 10 mm diameter polystyrene ball sprayed with black graphite paint is suspended from two threads which passes through the vertical slits in the blocks at the top of the sheet. The point where the ball hangs stationary can be adjusted by pulling the threads up or down through the slits in the polystyrene blocks. A 15 cm by 15 cm acrylic sheet, 5 mm thick, with more components on it, is fixed to the bottom of the mounting board with double sided tape. The ball hangs about in the middle of this sheet. I use a lab stand to keep the mounting board upright.

The two main parts of the electroscope are the threads and ball - that is the pendulum - and a copper strip. The successful operation of the electroscope is mainly due to the pendulum being quite long, about 75 cm, and it having a small mass. The mass of the ball is small due to the low density of both the polystyrene material and the graphite paint. The threads (monofilaments) also have a very small mass due to being extermely thin, about 30 microns or three-hundredths of a millimeter thick (measured with a micrometer). That is close to 1/20th of a millimeter thick. I snipped these threads from some synthetic material that was fraying a while ago, maybe it is nylon (anyone into experimenting and construction tend to collect a lot of special materials - fortunately I noticed that the threads were quite thin and long and decided to keep it rather than throw it away - just don't come and cry by me when your mother gives you a hiding). I also suspect that magicians use such threads to "invisibly" suspend objects like playing cards.

Here you can see the ball hanging up against the copper stem. The stem goes through a hole in the middle of the sheet and it is glued to it. An armband was used for the copper stem. One end of the stem was bent horizontal ( I intend to put a metal cup on it in some experiments). The sheet was clamped vertically in a vice while the resin holding the stem to the sheet was setting. A set square and two more clamps kept it in place during this time.The fact that the copper stem is thick and not too large also plays into the electroscope being quite effective. A piece of plastic ruler is also glued to a supporting block along the edge of the sheet. The ruler is used to measure the deflections of the ball when the electroscope is in use. I intend to show you how the electroscope is used in another instructable.