Fundamentals

There are some fundamental principles that one will have to understand and use in order to successfully analyze all seven Name That Charge situations. Those fundamental principles are ...

  1. Electrons are negatively charged and protons are positively charged.
  2. Only electrons are able to move during electrostatic charging processes.
  3. Opposites attract and likes repel. Thus, electrons are attracted to positively-charged objects and repeled by negatively-charged objects and by each other.
  4. If a neutral object gains electrons, then it becomes negatively charged. If a neutral object loses electrons, then it becomes positively charged.

 

There are a few nearly-identical versions of this question. Two of the versions include:
 

Version 1:

A neutral aluminum pie tin is brought near and touched to a negatively-charged Van de Graaff generator. After touching, what is the charge on the pie tin? What is the charge on the Van de Graaff generator?


A neutral object is touched to a charged object.



Version 2:

A neutral aluminum pie tin is brought near and touched to a positively-charged Van de Graaff generator. After touching, what is the charge on the pie tin? What is the charge on the Van de Graaff generator?


A neutral object is touched to a charged object.

 

How to Think About This Situation

This situation is an example of charging by conduction (or contact). Charging by conduction involves touching a neutral object to a charged object. Upon contact, the neutral object becomes charged as electrons move from one of the objects to the other. Once complete, both objects are charged with the same type of charge. To analyze this situation, you must carefully apply fundamental principles #3 and #4 listed above. You will have to answer the question: will electrons in the charged Van de Graaff generator move onto the neutral pie tin?  or Will electrons in the neutral pie tin move onto the charged Van de Graaff generator?