# Problem driving me insane electric forces

1. Jun 21, 2004

### supermenscher

When 2 identical ions are separated by a distance of 3.3*10-10m, the electrostatic force each exerts on the other is 8.5*10^-9N. How many electrons are missing from each ion?

I know I have to use coloumb's law to get Q1Q2, but how do i get the number of electrons missing from each?

2. Jun 21, 2004

### Staff: Mentor

The charges are identical, so Q1 = Q2 = Q. Solve for Q and figure out how many electron charges that it equates to.

3. Jun 21, 2004

### supermenscher

I solved for Q, but how do i convert to electron charges? Because Q comes out in Coloumb's squared

4. Jun 21, 2004

### Staff: Mentor

Not if you did it correctly. Show me how you applied Coulomb's law and solved for Q.

5. Jun 21, 2004

### supermenscher

Q = F*r*r/k
Q = 8.5*10^-9N *(3.3*10^-10m)^2/9.0*10^9 N*m^2/C^2
Q = 1.0825*10^-19 C^2
Q = square root of above = 3.207*10^-10C
What do I do after that?

6. Jun 21, 2004

### Staff: Mentor

You made an arithmetic mistake in finding Q*Q.

7. Jun 21, 2004

### supermenscher

can u explain youself a little more, i don't understand what you are trying to say in the above post

8. Jun 21, 2004

### turin

Hopefully DocAl will forgive my intrusion:

You are using the symbol, "Q," to represent Q1*Q2. But, if both Q1 and Q2 are equal to Q, then, upon substitution: Q1*Q2 = Q*Q.
It is at the very least symbolically misleading to say: Q1*Q2 = Q.

Anyway, once you get that straightened out, the charge will be in Coulombs. Then you need to use the charge of an electron in Coulombs: 1.6x10-19 C.