File: ELECSCOP.DOC

 

A DO IT YOURSELF ELECTROSCOPE

Background

One of the first good instruments for detecting charges was the electroscope. In this experiment you will construct one and use it to detect charges.

An electroscope is basically two connected light pieces of metal foil which are pushed apart by the repulsive force between like charges. You will get more out of the experiment if you read a description of an electroscope in your text and some reference books.

References

1. Crummet, W. P. and Western, A. B., University Physics (Modes and applications), advanced copy, (Wm. C. Brown, Publishers, Dubuque, IA, 1994) pp 614-615, 585-595.

2. Hewitt, P.G. Conceptual Physics, 7th Ed., (Harper Collins College Publishers, 1993) pp 372-377, 379-380.

3. Ostdick, V. S. and Bord, D. J., Inquiry Into Physics, 2nd Ed., (West Publishing Company, St. Paul, MN, 1991) pp 296-305.

4. Serway, R., Principles of Physics, (Saunders College Publishing NY, 1992) pp 435-438.

5. Tipler, P.A., Physics, 3rd Ed., (Worth Publishers Inc., NY, 1991) pp 601-607.

6. Young, H.D., Physics, 8th Ed., (Addison Wesley, NY, 1992) pp 607-609, 611-613.

Materials

Clean 16 Oz soft drink bottle

Paper clip

Foil from kit

Push pin

Instructions

Construct the electroscope following the numbered steps

1. Obtain a clear, 16 Oz. soft drink bottle with a plastic cap.

2. Drink the contents, remove the label (if it doesn't all come off don't worry), wash, and then rinse and dry the bottle.

3. Take a large paper clip, about 5 cm long, and fold out the long side leaving a U-shaped piece of wire with one side longer than the other as in the figure.

4. Round off the long end of the U-shaped wire with a fingernail file. (This step is not absolutely necessary.)

5. Punch a push pin through the center of the bottle cap from both the outside and the inside of the cap. You may have to wiggle the push pin to get the hole large enough for the next step. Do not make the hole so large that the paper clip will fall through.

6. Push the long end of the paper clip through the hole in the cap from the inside until it projects about 2 cm above the top of the cap. A drop of glue place on the cap and paper clip will help tip the position of the clip.

7. Place the foil from your kit on the paper clip U. It will help the stability of our foils

if you attach them together at the top with a very thin short piece of cellophane tape.

8. Gently lower the folded foil on the U into the bottle and screw on the lid. Your electroscope is now complete.

 

 

Now use your electroscope to investigate charged objects. Keep notes of what you observe because you will need a summary of the notes for your report.

Run a comb through your hair. Then bring the comb near the top of the paper clip. Watch the foils separate.

See how much change you can find in other situations. Walk across a rug, then bring your hand near the electroscope. Bring a piece of newly unrolled scotch tape near. Bring the electroscope up to a TV

screen or computer monitor. Rub the fur from your kit on the glass rod. Which is now charged?

Extensions

There are lots of additional ideas which you can investigate. Can you show that there are two kinds of charges?

Charge the electroscope by contact with one kind of charge. The foils will be separated. When you bring up other charged objects (without touching the electroscope) do the foils always go further apart?

Can you do some quantitative experiments? Is there a relationship between the distance the foils separate and the distance the comb is from the wire? How long does the comb hold its charge?

Report

The report should contain at least short statements about any difficulties you encountered in building the electroscope and a short paragraph on each of the charged objects you investigated. If you did any of the extensions, report the results in enough detail so that the reader can follow what you did.