question_answer

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 \[3d\] [IIT-JEE 1998]

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

Correct Answer: B

Solution :

 Even after introduction of dielectric slab, direction of electric field will be perpendicular to the plates and directed from positive plate to negative plate. Further, magnitude of electric field in air \[=\frac{\sigma }{{{\varepsilon }_{0}}}\] Magnitude of electric field in dielectric \[=\frac{\sigma }{K{{\varepsilon }_{0}}}\] Similarly electric lines always flows from higher to lower potential, therefore, electric potential increases continuously as we move from x = 0 to x = 3d.