Question

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 pates. The capacitor is given some charge. As one goes from 0 to 3d :

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

Answer 1

Answer: (C)

the electric potential decreases continuously

Even after introduction of dielectric slab, direction of electric field will also be perpendicular to the plates and directed from positive plate to negative plate. The magnitude of filed will be charged.
Before introduced dielectric the field between the plates $E=\frac{\sigma }{{ϵ}_0}$.
After introduced dielectric the field between the plates $E=\frac{\sigma }{K{ϵ}_0}$. where K is dielectric constant.
As electric field lines flow from higher potential to lower so potential will decrease continuously from $x=0$ to $x=3d$.