Need help finding electric field

[astru025]

Homework Statement

What is the electric field at a distance of 0.4 nm from a nitrogen nucleus containing 7 protons and 7 neutrons?

Homework Equations

I got the answer 6.3E10 but I do not remember how I got to that answer and now I need to do this same problem but at a distance of .2 nm instead of .4 nm! Any help would be nice!

The Attempt at a Solution

Thanks!

 

[MalachiK]

You need to look up the formula for the strength of a radial electric field (field due to a point charge). Try hyperphysics or just plain old google. You'll also need to know the charge on a proton to put into your calculation.