# What is 'K' in K=1/4pi Epsilon 0?

Hey So for those that don't know, I'm reading this from Atomic Physics, basically where they teach you how the size of a nucleus was determined by shooting alpha particles at it. due to repulsion an alpha particle can get only 'so-close' to nucleus(they're both positively charged), and the the so-close is labelled as point P, the closest to the nucleus and alpha gets.

So heres a formula they teach us to use:

1/2mv2 = kQq/r

What is k called? what is the name of this constant, and what is it equal to since I was told it was the electric constant and went about solving it with that value, but at the back in the answer section they used the value 9x10^9!!
Thanks guy!!! :D

tiny-tim
Homework Helper
hi kenshi64! that's the https://www.physicsforums.com/library.php?do=view_item&itemid=114" equation

k (or ke) is the Coulomb constant, 8.988 109 Nm2/C2

k = 1/4πε0

ε0 (not k) is the electric constant, also called the permittivity of the vacuum

see http://en.wikipedia.org/wiki/Coulomb%27s_law" [Broken] for more details Last edited by a moderator: