Difference between These Electric Field Formulas

[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
$$E = \frac{\omega}{\epsilon_0}$$
on the other hand the notes from my prof tell me that
$$E = \frac{\omega}{2\epsilon_0}$$

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?

 

[Kidphysics]

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.html#c2

 

[wahaj]

so basically the first equation is for an infinite plane while the second one is for a plate with a definite length like in a parallel plate capacitor. Did I get that right?

 

[Redbelly98]

Not quite. One formula (with the "2" in the denominator) is for a single sheet, the other is for the field between two oppositely charged sheets. One way to remember this is that having two sheets produces twice the field, which gets rid of the "2" in the formula.

In both cases the sheets are considered to be very large compared to the distance away from the sheet.