A dielectric slab of thickness `d` is inserted in a parallel plate capacitor whose negative plate is at `x = 0` and positive plate is at `x = 3d`. The slab is equidistant from the plates. The capacitor is given some charge. As one goes from 0 to `3d`:

Options

A. the magnitude of the electric field remains the same
B. the direction of the electric field remains the same
C. the electric potential increases continuously
D. the electric potential increases at first, then decreases and again increases

Explanation

In regions I and III there will be electric field `vecE_(0)` directed from positive to negative in region II due to orientation of dipoles there is an electric field `vecE_(0)` present in the opposite direction of `vecE_(0)` but since `vecE_(0)` is also present the net electric field is `E_(0)-E_(k)` in the direction of `vecE_(0)` as shown in fig. `(becauseE_(0)gtE_(k))`
Also, please note that when one moves opposite to the direction of electric field the potential always increases, the stronger the electric field the more is the increase in potential sice in region II the electric field is less as comparred to regions I and III the increase in potential will be less but there has to be less but there has to be an increase in potential in all the regions from `x=0` to `x=3d`.