Charged Sphere Question: Understanding Charge Transfer When Two Spheres Touch

[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?

 

[gabbagabbahey]

Say you have a -vely charged sphere, you bring it close to a neutral sphere. Now the neutral sphere becomes +vely charged.

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

 

[likephysics]

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

 

[gabbagabbahey]

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

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?

These are questions you need to ask yourself in order to answer your query.

 

[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.

 

[gabbagabbahey]

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.

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?

 

[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.

 

[zoobyshoe]

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.

So the neutral sphere is a conductor (otherwise the charges would not be free to move around) ...

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

A pith-ball electroscope, invented by British weaver's apprentice John Canton in 1754,[2] consists of a small ball of some lightweight nonconductive substance, originally pith, suspended by a silk thread from the hook of an insulated stand. In order to test the presence and magnitude of a charge on an object, the object is brought near to the uncharged pith ball.[3] If the object is charged, the pith ball will be attracted to it.

This attraction occurs because of induced polarization of the atoms in the pith ball. The pith is a nonconductor, so the electrons are not free to leave their atoms and move about the ball, but they can move a little within the atoms. If, for example, a positively charged object is brought near the ball, the negative electrons in each atom will be attracted and move slightly toward the side of the atom nearer the object. The positively charged nuclei will move slightly away. Since the negative charges are now nearer the object than the positive charges, their attraction is greater than the repulsion of the positive charges, resulting in a net attractive force. This separation of charge is microscopic, but since there are so many atoms, the tiny forces add up to a large enough force to move a light pith ball.

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