# Homework Help: Electrostatics Lab Analysis

1. Feb 17, 2016

### cvc121

1. The problem statement, all variables and given/known data
Based on a lab we did at school, we charged a Styrofoam plate by rubbing it against wool and determined that it attracted pieces of paper but repelled pieces of aluminum foil. Can anyone clarify why this is because I believe that both the pieces of paper and aluminum foil are neutral so wouldn't they both attract?

2. Relevant equations
N/A

3. The attempt at a solution
My only reasonable explanation is that the aluminum foil is conductive and picks up the electrons from the negatively charged Styrofoam plate and repel while the pieces of paper which act as an insulator attract to the plate. All help is very much appreciated!

2. Feb 17, 2016

### ehild

You are on the right track. The charge can not move in the paper pieces, it stays polarized by the Styrofoam, but neutral, while the aluminium foil gets charged as it is in contact with the Styrofoam for a very short time,

3. Feb 17, 2016

### Staff: Mentor

Was the foil seen to be first attracted to the plastic plate?

4. Feb 17, 2016

### andrevdh

You are very much right cvc.
Intitally they are both attrackted, but upon contact the foil gets charged up and then repelled.
Why would the paper react differently?
Why are they both intially attracted?
Note that sometimes even the paper is repelled after a while. So these conditions or outcomes are not always the same for pieces of paper, but the foil will always act in the way descirbed. Any idea why?
Keep in mind that the styrofoam is also a nonconductive material.

5. Feb 17, 2016

### cvc121

Thanks for the replies everyone! Am I on the right track in saying that the negatively charged Styrofoam plate repels the free electrons on the surface of the neutral pieces of paper that is nearest, moving them to other parts of the object. Hence, this leaves a new positive charge on the side facing the negatively charged Styrofoam plate, and the two unlikes attract.

6. Feb 18, 2016

### ehild

The paper is not a conductor, it has no free electrons. Its electrons are bound to the molecules, they can not leave their molecules and moving to other parts of the paper.

7. Feb 18, 2016

### cvc121

Ok. So how else are the paper pieces able to attract the negatively charged Styrofoam plate since no movement of electrons take place?

8. Feb 18, 2016

### andrevdh

The molecules in the paper are polarized by the electric field generated by the charged styrofoam plate.