Question

Why is the direction of E field inside a Linear Dielectric same as an external field?

Answer 1

Electromagnetic waves are made up of photons (dual nature consideration). Photons do not interact with other photons. For example,  the light from this screen is not just going in your eyes, but everywhere else around the room. But the other photons do not block light that is falling om your eyes. Since the external field you apply are basically photons, they do not affect the photons moving through them.

Answer 2

Explanation:

• A dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving in the positive x-axis, the negative charges will shift in the negative x-axis). This creates an internal electric field that reduces the overall field within the dielectric itself.[1] If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.[1]