# Confusion on the definition of dielectric permittivity

I don't understand how we're defining the dielectric permittivity, sometimes it's defined as the ability of the material to resist the electric field and sometimes as the ability to permit the electric field to pass through. Can anyone please clarify this confusion?

• Hello @Manish Parmar. Welcome to Physics SE. What you say above are just words. Equations usually matter more, so I would suggest to start there. How do you use permittivity in Maxwell's equations? As for words, I would simply say that "permittivity describes how matter responds to applied electric field" whether it is resist or permit is not that important.
– Cryo
Commented Jun 21 at 6:07
• The physical vacuum lets the electric field "pass through". A dielectric always modifies the field compared to the vacuum field. I wouldn't chose the word "resist" in this case because it implies (at least in my understanding) dissipation and insulating dielectric materials are not really dissipative for static electric fields. Beyond that it can get complicated rather quickly because now we are talking about materials that have microscopic degrees of freedom and that allow for a very large number of physical effects but the most simple of these effects is a bulk dielectric constant. Commented Jun 21 at 6:17

Dielectric permittivity quantifies how much do the dipoles inside a material want to get polarised ie how much do they want to align with an applied electric field such that the induced electric field within the material opposes it.

There are two ways or two senses in which we can think about it:

• “resistive” sense: this sense deal with how much the material decreases the strength of an external electric field passing through.
• “permissive” sense: this sense deal with how readily an internal electric field will be created to oppose the external field inducing it. This sense is more commonly thought of when talking about dielectric permittivity.

Both definitions are correct but we must expand on how exactly it is correct.

I hope this helps!