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Home Concept Builders Static Electricity Charge Interactions Help Help 4

Charge Interactions - Questions 4 Help

The type of charge an object possesses can be determined by observing its interactions with other objects of known charge. Objects that possess opposite types of charge will be observed to attract each other. Objects that possess the same type of charge will be observed to repel each other. And a neutral object and a charged object will always attract each other.

There are two similar versions of this question. Here are the two versions:

Version 1:

Object A is positively charged. Object A and Object B attract. Object B and Object C attract. Object C and Object D repel. What type of charge does Object B, Object C, and Object D possess?
 
Version 2:
Object A is negatively charged. Object A and Object B attract. Object B and Object C attract. Object C and Object D repel. What type of charge does Object B, Object C, and Object D possess?

You have some thinking to do. The physics is straight-forward: opposites attract, likes repel, and charged and neutral attract. But the application of these simple rules can get complicated. Get yourself a scratch paper to jot down some notes as you do your thinking.

The Game Plan
You will need to start with the A-B interaction since you know the charge on A. Use this charge and the interaction with B to determine the possibilities for the type of charge on B. Then repeat for Object C and then for Object D.

Careful about Attraction
There are two reasons for why two objects attract. They could be oppositely charged or one could be charged and the other be neutral. And so when you read that A and B attract, that means B could be charged (opposite of A) or neutral. You will not know which it is until you have more information about B's interaction with another object. When you read that B also attract C, then you can not be any more conclusive about B's charge. There remains two possibilities - it is either neutral or charged the opposite of A.

Repulsion Provides Evidence for Clear Conclusions
There is only one reason for why two objects repel - they have the same type of charge. Neutral objects can never be involved in repulsion. So when you read that C and D repel, you know that they are both charged and charged with the same type of charge. Repulsion always leads to very clear conclusions about the charge type of objects. Unfortunately, since the type of charge on C and D is not known, all that can be concluded is that both of these objects are charged - either positively or negatively.

Try this link to The Physics Classroom Tutorial for more help with understanding charge interactions:

Charge Interactions

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