P201 Menu


Will That Be Cash Or "Charge?"


How many types of electrical charge exist and how do they interact with each other?


Sheet of colored paper, small sheet of scrap paper, scraps of cloth, aluminum foil and styrofoam, comb, salt and pepper, transparent tape, and a ring stand with a non-metal crossbar.


Part A

1. Make at least ten very, very small pieces of white paper from the scrap paper.
Place these on the colored paper. Then sprinkle a small amount of salt and pepper
on the colored paper. Align the teeth of the comb parallel to the desk top and
slowly move the comb close to the paper, the salt, and the pepper. Observe what
happens and record your observations.

2. Now vigorously rub the comb back and forth several times with a piece of cloth.
Again, slowly move the comb towards the paper, salt and pepper. Once more
observe what happens and record your observations.
Repeat with a different type of cloth or other material. Record your observations.
Suggest and try other variables beside cloth that might be changed. See your
teacher for additional materials. Clean up the materials.

3. Predict what will happen if you substitute tiny bits of aluminum foil and
styrofoam for the salt and pepper. Now test your prediction. Keep the colored
paper and the small pieces of white scrap paper. You will need these for Part B.

Summing Up:

Part A

1. What happened when you brought the rubbed comb close to the paper, salt and
pepper? What explanations can you offer for why this happened? Were all three
substances affected equally?

2. What combinations of cloth and comb or other objects or materials seemed to
produce the greatest effects?

3. You actually created an electrical charge on the combs that were rubbed. In light of what you know about atomic structure, explain whether electrons or protons were being transferred when the comb was rubbed with cloth or fur.