Question

What is the electric field due to the two charged plates in parallel plate capacitor why is it added in deriving the capacitance of capacitor.

Answer 1

In capacitor, there are two plates with opposite charge on it i.e. one is positively charged and other is negatively charged.
Electric field due to positive charged plate acts away from the plate and due to negatively charged plate acts towards the plate.hence both act in same direction.
Therefore at a point inside the capacitor, net electric field is sum of the electric fields due to both the plates.
$$\begin{gathered} electricfieldguechargedplate \\ E=\frac{\sigma }{{\epsilon }_o} \\ where\sigma isthesurfacechargedensityoftheplate. \end{gathered}$$