# Force between two electrons

Okay so I'm working on a question for practice and I'm sure I'm getting the right answer but the answer they give me is something different. Anyway the exact question is:

An electron is located at the origin of the coordinates, and a second electron is brought to a position 2 Angstroms from the origin. Calculate the force between the two electrons.

I'm guessing I need to use the equation:

F(r) = (q1*q2)/(4*(pi)*e*r2)

Where q1 and q2 are the magnitude of the charge of the electrons, which I'm taking to be e2 or (1.602E-19)2

Where pi is pi, ie 3.14159....etc

Where e is the vacuum permittivity constant, 8.854E-12

Where r is the distance between the two electrons in meters which I'm taking to be 2E-10 since 1 angstrom is 10-10 meters

Anyways I do the calculations and I'm getting 5.7666E-9 Newtons but in the back of the problem book it says the answer is 7.1999E-9 Newtons

It's close but I'm wondering if there's some trick to the problem or something I missed. Can someone confirm or dispute if I'm doing this correctly?

Delphi51
Homework Helper
I get 5.75. Used Coulomb's constant k = 8.99 x 10^9 instead of your 4*pi*ε.

I get 5.75. Used Coulomb's constant k = 8.99 x 10^9 instead of your 4*pi*ε.

both k and 1/4*pi*ε are same ...

and i am also getting same answer i.e. 5.76 nN
so it seems the book is wrong somewhere