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Contents 1 Introduction: What is an Electroscope? 2 How to Build Your Own Eletroscope 3 Materials 4 Directions 4.1 How to Charge the Electroscope

Introduction: What is an Electroscope?

The basic idea of an electroscope is that two metal strips will repell each other when charged, or charge is induced. Historically electroscopes were used to perform a number of experiments and important discoveries. The pioneer work of Victor Hess that lead to the discovery of cosmic rays, was done by verifying how fast electroscopes would discharge as function of altitude.

How to Build Your Own Eletroscope

The following design uses conventional materials and can be used for several different demonstrations.

Materials

• Pretzel jar
• Aluminum foil
• Copper wire
• Rubber stop (or cork)
• Copper plate (optional)

Directions

Choose the thinnest aluminum foil possible. The way in which we determined this was by a comparison between those that had the same yardage. The lightest one is what we want, which conveniently is usually the cheapest. Cut two long,thin strips.

Make a hole in the lif of the plastic jar. It is easier and safer if you use a cup saw with the diameter of the rubber stop. If you don't have anything similar to a cup saw, you use an Exacto knife with caution. Then insert the rubber stop. It is not necessary to epoxy it in place, but you got the idea. The fit should be snug but not permanent. Next, Insert the copper wire through the hole in the rubber stop. Bend the portion inside the jar into a small hook shape. This is where the aluminum strips are CAREFULLY hung.

(In the electroscope pcitured above, we soldered a copper plate. It requires a lot of heat to solder the copper plate - use a torch. It is easier to solder the wire and the plate before inserting it into the rubber stop.)

Voila! You have a giant eletroscope!

So why do we need the jar? The jar is needed to protect the apparatus from interference such as wind. More importantly, the two pieces of foil must not touch each other. What is the top plate for? Well it is for experiments.

How to Charge the Electroscope

Usually electroscopes can be charged if humidity is low. On a typical summer day (assuming you live on the East coast) you won't be able to charge the electroscope. So this is a winter activity. To charge an electroscope you will need a rod (pvc or lucite) and a piece of felt. Your degree of sophistication varies. Give the lucite or PVC pipe a good rub with the felt to charge is with static electricity. Now, when you bring the end of the rod near the surface of the copper plate you should see the two leaves of aluminum reppel each other. Similarly, when the rod/charge is removed, the two pieces should return to their initial position. Why? Answer: The charge was induced. To charge it permanently bring the rod near to the plate, with your finger, or better yet a grounded wire touch the top of the plate. The two leaves will collapse and when you remove the rod they will come apart. This is how you know that the electroscope is charged!

Another fun way to charge the electroscope is with Scoth tape, masking tape or electrical tape. Stick the tape on the plate. Without touching the plate remove the tape quickly (rip it). Some electrons are removed during this rapid motion - yes the bond between the tape and copper plate is due to electrons.

If you have any other variations of the experiment or innovative ways to use the Preztelscope please add it to the Wiki entry. Thanks!

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