wahaj

just a quick question. I seem to have come across two very similar formulas for electric fields produced by uniformly charged parallel plates. My book gives the formula as
[tex] E = \frac{\omega}{\epsilon_0} [/tex]
on the other hand the notes from my prof tell me that
[tex] E = \frac{\omega}{2\epsilon_0} [/tex]

My book or the notes don't mention the other formulas and this whole concept is still new to me to I'm a bit confused. what is the difference between the two formulas?