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Transfer of charges between 2 conductors

  • Thread starter pizzadude
  • Start date
8
1
Hi. If a conductor (A) touches another highly charged conductor (B) such as one on the Van De Graaff generator, then I move conductor A via a string away from conductor B. Does conductor A retain the charges that it had gained when it touched the highly charged conductor?

If conductor A does retain the charges, then why does a person touching the Van De Graff generator does not get electricuted when he steps off the insulating platform and onto the ground. Shouldn't the charges that he retained move from his body to the ground and hurt him?

Similarly, if conductor A touches the positive end of say a 100V DC battery, will there be any charges flowing from the battery to conductor A and remain there even after conductor A has been removed from the battery?

I appreciate anybody's help to clarify this for me.

Thanks
 

Answers and Replies

vanesch
Staff Emeritus
Science Advisor
Gold Member
5,007
16
Hint: think about "capacity".
 
8
1
Thanks vanesche. Actually, I did think about capacity when I wrote the questions. I know that the closer the positive and negative plates are in a capacitor, the more charges they can hold given a certain potential difference. So that means that it takes the negative charges nearby to keep the positive charges from going away and vice versa for the positive charges.

I am thinking that maybe your hint implies that there are no transfer of charges between two conductors without maybe another negative conductor nearby. But I ran into a problem in the book where it asks me what the ratio of the charges on two metal spheres is when they are connected to each other. That problem would mean charges do transfer from one positive conductor to another (say) neutral conductor. Doesn't it?
 
8
1
Based on the capacitance formula for a parallel-plate capacitor: ( C=EoA/d ), capacitance would equal 0 as distance between the plates approaches infinity. That means the plates would not hold any charges when they are connected to a battery if the plates are really far away from each other.

But I've read of so many instances where charges do transfer from one conductor to another conductor without a loop (like the charge of one isolated conducting sphere going over to another conducting isolated sphere when they're connected by a wire).

So, I'm confused by what seems to be contradictory circumstances. One is charges from a battery do not seem to go over to plates that are really far apart and the other is charges from one conducting sphere do go over to another conducting sphere no matter how far apart those spheres are as long as they're connected by a wire.
 

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