Why is electric field stronger in vacuum than in a medium?

[Danen]

So I just wanted to clarify:

Because D = ε0E + P

P being zero in vacuum
and ∇D is constant regardless of medium

if D was originally in a vacuum, the corresponding E would be greater than if it were in an insulating medium. So,

E in vacuum > E in medium

 

[mfb]

Not if you use materials where P is opposed to the direction of the electric field. That can happen in metamaterials for oscillating electromagnetic fields of specific frequencies.

 

[Danen]

Thanks for clearing that up mfb.