# Question on electric charges

1. Feb 11, 2014

### asdff529

Suppose we have two insulated uncharged metal spheres,say X and Y, in contact with each other.A negatively charged object C is brought near X
My first question is:Do all of the electrons move to the sphere Y since electrons are free to move?
Then if X is touched momentarily with a finger,and then X and Y are separated.
My second question is:What are the charges on X and Y now?Why?
Also,what are the movement of the electrons?I mean do they move from the Earth or the sphere,or from the sphere to the Earth?Why?

2. Feb 11, 2014

### Staff: Mentor

First question: no, not all of the free electrons will move. If they all bunched together on the other sphere, there would be great repulsion forces sending most of them back to X.

Second question: what do you think? We need your thoughts on what is going on.

This thread will probably be moved to the homework subforum, as your questions resemble a homework-type exercise.

3. Feb 14, 2014

### asdff529

um....if i treat the spheres as a big thing,this 'big thing' will become positively charged as it is charged by earthing.Then when these spheres are separated,since sphere X is the one touched by the finger,it will become positively charged.But i ain't sure what the charge of Y is.
Also,the electrons,I think,will move from the spheres to the Earth as the spheres with C is at a lower potential,electrons will move from the lower potential to higher potential,which I was taught.But,again,how 'much' electrons are transferred during this process?Do we able to determine it?

4. Feb 14, 2014

### Staff: Mentor

At what point in this sequence is body C removed from the picture?

5. Feb 19, 2014

### asdff529

it doesn't specify at what point body C is removed from the picture

6. Feb 19, 2014

### Staff: Mentor

The scenario sounds right, as far as you described. The presence of nearby negative charge sends some electrons away from that region of X. When you touch X or Y those repelled charges can escape to earth, leaving X and Y uncharged except for an area on X directly under the influence of that field from C. What would be the polarity of the charge on that area of X near to C?

Then, what happens when you move C far away, but you keep X and Y still touching?

7. Feb 27, 2014

### asdff529

If C is still near the X,the space near C will have positive charge.After C is removed and my finger is still touching the sphere,the two spheres will become neutral,am I correct?

8. Feb 27, 2014

### Staff: Mentor

That would happen. But that's not what I'd understand by "touched momentarily".