# Count the Electrons

#### Due Friday, Dec 20, at 5 PM.

This project must be done by individuals. The goal is to calculate the number of excess electrons on a piece of tape.

The basic idea:

1. Cut two pieces of scotch tape from a roll. Make each a few inches long.

2. Carefully hold them so that each hangs down vertically, and bring them close to each other -- within an inch or so, but without touching. They ought to continue to hang straight down, since each one should be neutral.

3. Now, one at a time, press each piece of tape to a tabletop and then rip it off.

4. Once again, let the pieces hang vertically and slowly and carefully bring them towards each other. As they get very close, you should see one or both pieces bend outwards, away from the other.

5. Find the separation which causes one (or both) pieces to bend at roughly forty-five degrees from the vertical. Measure this separation.

6. Measure the mass of the piece of tape. For reference, a paperclip has a mass of about one gram. You might cut a long piece of tape and weigh it on a scale, then use ratios to determine the mass of the short pieces of tape.

7. Figure out the gravitational force downwards on the piece of tape. When the tape hangs at 45 degrees, the force downwards (due to gravity) is equal to the force sideways (due to electricity).

8. Estimate the size of the electric charge on each piece of tape.

9. Estimate the excess of electrons on each piece of tape.

Submit a report which contains a description of your method, with a clear drawing and all relevant dimensions, masses, etc. Include the data for your experiment, and all calculations. You may also include interesting items you discovered during the course of the procedure.