# How should I approach this question?

1. Jan 18, 2006

### matt85

A K+ ion and a Cl- ion are directly across from each other on opposite sides of a membrane 7.9 nm thick. What is the electric force on the K+ ion due to the Cl- ion? Ignore the presence of other charges.

_____N

Thanks,
Matt

2. Jan 18, 2006

### fargoth

hmmm... do you know coulomb law? $$E=\frac{q}{|r_1-r_2|^2}$$
and $$F=qE$$

3. Jan 18, 2006

### matt85

Yes, but all that is given in the problem is "r". How do I find "q"?

4. Jan 18, 2006

### darkar

The q is just the value of -e i think.

5. Jan 18, 2006

### Tide

HINT: What do the "+" and "-" mean in K+ and Cl-?

6. Jan 18, 2006

### matt85

Ohhh, ok. Thanks a bunch guys.

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