Charged sphere question

1. Jan 23, 2009

likephysics

Say you have a -vely charged sphere, you bring it close to a neutral sphere. Now the neutral sphere becomes +vely charged.
What happens if you touch the 2 spheres (sphere 1 touches sphere 2)?
Do the charges get recombined, with net charge=0?

2. Jan 23, 2009

gabbagabbahey

Why would the neutral sphere become +vely charged? How did the positive charge get there, and where did it come from?

3. Jan 23, 2009

likephysics

The neutral becomes +ve, because of induction (from the -vely charged sphere).

4. Jan 23, 2009

gabbagabbahey

Okay, but why is there a charge induced? Is the sphere grounded? If not, where is the charge coming from? From the -vely charged sphere? How is the charge getting to the sphere?

5. Jan 23, 2009

likephysics

Charge is getting induced because of electrostatic force.
The sphere is not grounded. The +ve charges come towards the 1st sphere, the -ve move away from the first sphere.

6. Jan 23, 2009

gabbagabbahey

So the neutral sphere is a conductor (otherwise the charges would not be free to move around) that stays neutral (at least until the charged sphere touches it). The net charge on the neutral sphere will be zero until it is contacted by the charged sphere. Just because the positive charges are closer to the charged sphere, does not mean that the neutral sphere is positively charged.

This means that before the spheres touch each the net charge of the two sphere system is just whatever charge is on the negatively charged sphere (call it -Q) correct? Given that charge is conserved, what must the net charge for the two sphere system be after the spheres touch? If one sphere had more charge than the other would there be a force? If so, what would that force do to the charges?

7. Jan 23, 2009

KnowPhysics

Yes the charge will recombine. the neutral sphere will have equal +ve and -ve charges when you are getting '-ve' ly charged sphere close to this neutral sphere all the +ve charge will get attracted towards the -ve sphere and same way all negative changes will be repelled from -ve charges. when you touch both whole thing becomes one object and there is no need of induction the charges can freely move so it will be recombined.

8. Jan 23, 2009

zoobyshoe

His post might also be describing induced polarization of the atoms in an insulator. The same toward/away description fits:

http://en.wikipedia.org/wiki/Electroscope