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## 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

## Homework Equations

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.