# Static Electricity

1. Oct 8, 2009

### DarkPhoenix

1. The problem statement, all variables and given/known data

https://www.physicsforums.com/attachment.php?attachmentid=21003&stc=1&d=1255013927

I need help for number 11(b), (d)

3. The attempt at a solution

(b)(i) Electrons move towards the right since like charges repel.
(ii) Unlike Charges attract. Thus, positive charges from sphere are attracted to rod.

2. Oct 8, 2009

3. Oct 8, 2009

### DarkPhoenix

(b) An uncharged metal-coated sphere hangs from an insulating thread. The sphere is brought
near to the rod. The sphere is attracted to the rod, as shown in Fig. 11.1.

(i) Describe and explain what happens to the free electrons in the metal-coated sphere as it
approaches the rod.
(ii) Draw a diagram to show how charge is distributed on the sphere.
(iii) Explain why the uncharged sphere is attracted to the negatively-charged rod.

(d) Describe one device where electrostatic charging is used. In your answer include a
diagram and explain how and why the charge is produced.

4. Oct 14, 2009

### tiny-tim

Hi DarkPhoenix!
(i) Yes.

(ii) ah, but surely the negative charges from the sphere are repelled from the rod; and there are an equal number of positive and negative charges; so why doesn't all the attraction and repulsion cancel out?