# Help needed! (electric fields)

1. Sep 14, 2006

### avb203796

An iodine (-1) and a chloride ion (-1) interact in a vaccum.

a. What is the force which each exerts on the other from a distance of 2.0 x 10^-9 m?

b. What is the eletric field that the iodine ion experiences from the chloride ion? toward which ion does the electrical field vector point?

c. By what factor must the chloride ion be moved so that it experiences 1/64 of the electric field iodine ion as in part b?

This is work from the spring that I am finishing up and I can not rember how to go about solving this problem. Could someone please help me? I just need a poitn in the right direction.

I am pretty sure that the forces they exert on each other would be equal but beyond that I am not sure how to go about the problem.

Last edited: Sep 14, 2006
2. Sep 14, 2006

### Kurdt

Staff Emeritus
The force between two charges is given by:

$$F=\frac{1}{4\pi\epsilon_0}\frac{Q_1Q_2}{r^2}$$

and the electric field for a point charge is given by:

$$E=\frac{Q}{4\pi\epsilon_0r}$$

just a case of plugging in the numbers.

3. Sep 14, 2006

### avb203796

so does that mean my force would be = 5.77 X 10^-11

4. Sep 14, 2006

### Kurdt

Staff Emeritus

5. Sep 14, 2006

### avb203796

should my Q1 and my Q2 have the same number because they both have a negative charge?

6. Sep 14, 2006

### Kurdt

Staff Emeritus
I'm not sure what you mean but I assume that you're talking of parts a and b and they will have opposite signs because both ions are negatively charged.

7. Sep 14, 2006

### avb203796

I guess what I am trying to figure out is what the Q1 and Q2 are in the force formula?

8. Sep 14, 2006

### Kurdt

Staff Emeritus
Oh I see. Yes Q1 and Q2 will be the same value because both ions have a negative charge of one.

9. Sep 14, 2006

### avb203796

so then the mass of the ions is irrelevent? because my teacher did say as a hint to remember that ion charges are multiples of the charge on an electron, and their masses in atomic weights are multiples of the mass of a proton

10. Sep 14, 2006

### Kurdt

Staff Emeritus
No mass is needed in this problem as far as I can see.