# Electric Charges and Fields

1. Dec 6, 2009

### LampMan

1. The problem statement, all variables and given/known data
two charged spheres 4 cm apart attract each other with a force of 1.2x10^-9 . determin the magnitude of the charge on each if one has twice the charge (of the opposite sign) as the other.

2. Relevant equations

Fe = KQq/r^2

3. The attempt at a solution

well you are only given Fe and r, plus the info that Q is = to (2)q and k = 9.0x10^9 so im stumped after this step

1.2x10^-9 = (9.0x10^9)(2)qq/16

Last edited: Dec 6, 2009
2. Dec 6, 2009

### kuruman

In your equation everything is a number except for q. Can you solve it for q? Also, you forgot to convert cm to meters.

3. Dec 6, 2009

### LampMan

could it possibly be that im using the wrong equatiom? and should be using E(force intensity) = kq/r^2 instead of coulombs law??

edit: yes i forgot to convert haha good call..but yea the fact that im finding two charges throws me off...so would just solving for one q give me the charge im looking for, then just double it to get the 2nd charge?

4. Dec 6, 2009

### kuruman

Correct. Find q then double it. It is that simple.

5. Dec 6, 2009

### LampMan

aha well ive mised 2 of 2 classes on this unit so i cant believe it was that easy now that i see it ahhh well thanks alot