# Electric force question help

1. Aug 20, 2008

### Velocity.

Electric force question help plz!!

I was just doing a question in my text book and I got stuck on this question as my answer is no where near the given answer.

Two charges of magnitude 0.24 μC and 0.29 μC are in a liquid dielectric with dielectric constant κ = 2.0. The charges are separated by a distance of 0.42 m.

(i) What is the size of the electric force between the charges?

I got an answer of 3.314e-13N whilst theirs is 0.00177N

What am I doing wrong?? I'm using the F=kq1q2/r^2 formula, substituting 0.24 and 0.29 for q1/q2, using 2.0 as k and 0.42 for r.

2. Aug 20, 2008

### ak1948

Re: Electric force question help plz!!

Recheck your formula; its quite wrong. For one thing, the permittivity constant is missing. Also do you think the electric force between charges is increased by placing a dielectric between them?

3. Aug 20, 2008

### Redbelly98

Staff Emeritus
Re: Electric force question help plz!!

The k constant in "F=k..." is different than the "k" (or Greek kappa?) used for the dielectric constant.