# Problems involving electromagnetism

## Homework Statement

In problems involving electromagnetism it is often convenient and informative to express answers in terms of a constant, x, which is a combination of the Coulomb constant, k, the charge of an electron, e, and H=h/(2pi), with h being Planck's constant. For instance, the lowest energy that a hydrogen atom can have is given by E=-(0.5)(x^2)m(c^2), where m is the mass of the electron and c is the speed of light. Which of the following is the correct expression for x?
(HINT: Non-relativistic kinetic energy is (0.5)m(v^2), where v is the speed.)

a) (k(e^2))/(Hc)
b) H/(k(e^2)c)
c) (k(e^2)H)/c
d) (k(e^2)c)/H

E=hf
E=m(c^2)
E=(1/2)m(v^2)

## The Attempt at a Solution

I really don't know what they are asking for or what formula they are referring. Can someone help? Thanks.