# Homework Help: Negative rod to uncharged metal ball:

1. Jan 26, 2008

### sonastylol

[SOLVED] negative rod to uncharged metal ball:

1. The problem statement, all variables and given/known data
If a negatively charged rod is held near an uncharged metal ball, the metal ball:
1. becomes positively charged.
2. becomes polar.
3. Effect cannot be determined.
4. becomes negatively charged.
5. is unaffected.

3. The attempt at a solution
I guessed number 4, thinking that if the negative rod touched the neutral ball, the ball would gain electrons ( since its easier to gain and lose electrons - very very difficult and rare for an object to lose or gain protons )

This would make the ball negative but I was wrong... whats the catch here?

2. Jan 26, 2008

### Mindscrape

The negative rod does not touch the ball though. What do you know about the electric field inside of a conductor?

3. Jan 26, 2008

### sonastylol

oh my god. i read it as touched.

IT NEVER TOUCHED X_X

4. Jan 26, 2008

### sonastylol

there is no change - no contact was ever made.

5. Jan 26, 2008

### sonastylol

wait, unaffected is the wrong answer x_x now what am i missing?

wow - yikes... is it not determinable?

6. Jan 26, 2008

### sonastylol

The answer is it becomes polarized ; the ball has an effective separation of charge

7. Jan 26, 2008

### Mindscrape

Yes you could get the answer by knowing that inside the conductor that the electric field must be zero. So when the negative rod goes towards the conductor, then a bunch of positive charges need to go towards the end the rod approaches, and then negative charges must accumulate on the other side. It polarizes.