# I Coulomb's law in its vector form?

1. Oct 25, 2016

### ConfusedRookie

sorry I have use the image I made. Since I don't know how to perform the formula on forum :(
This is the problem I am having.

Last edited: Oct 25, 2016
2. Oct 25, 2016

### BvU

Hello Rookie,

You would miss the direction of $\vec F$ if one of the two charges has a charge opposite to the other...
In other words: $\vec F$ can be in the same direction as $\vec r$ or it can be in the opposite direction.

3. Oct 25, 2016

### ConfusedRookie

4. Oct 25, 2016

### ConfusedRookie

Oh my god. I've just realized without the absolute symbols. It would be more easier to express the direction. Oh my oh my thank you very much teacher :)

5. Oct 25, 2016

### BvU

My pleasure

6. Oct 25, 2016

### ConfusedRookie

Teacher. There's one more thing I would like to ask. I see there are many formular using "charge density". Is charge density able to be negative !?

If a charge density can be negative, it is very much easy to express its direction. I didn't find any vector form E that use the unit vector to express direction. They mainly focus on the magnitude.

7. Oct 25, 2016

### BvU

With $\vec F = q\vec E\$ you can use (almost) the same expression

Charge density can be negative, yes: negative charge leads to negative charge density

Your picture in post #6 comes through as a lot of letters/numbers

8. Oct 25, 2016

### DrGreg

Click HELP at the bottom of any page and then LaTeX Primer.

9. Oct 30, 2016