# “dielectric constant” or “electrical permittivity”?

What are the differences between "dielectric constant" and "electrical permittivity"?

By searching on the net, I found permittivity = absolute permittivity, which is the measure of capacitance that is encountered when forming an electric field in a particular medium. The lowest permittivity is that of a vacuum: vacuum permittivity = electric constant. In addition, relative permittivity of a dielectric medium is represented by the ratio of its absolute permittivity to the electric constant.

Therefore, I think the "electrical permittivity" in many literatures should be equivalent to absolute permittivity above. But what is "dielectric constant"? Any suggestion?

• What did you not understand about the definitions given at the beginning of the Wikipedia link that you provided? It clearly states that dielectric constant is another name for relative permittivity, and both are simply the ratio of absolute permittivity to the permittivity of free space, $\epsilon_0$. – amateurAstro Jul 3 '19 at 13:14

The dielectric constant is the same thing as relative permittivity and is equal to the ratio of the electrical permittivity of a material to the electrical permittivity of a vacuum, or

$$ε_{r}(ω)=\frac{ε(ω)}{ε_o}$$

The electrical permittivity is generally a function of frequency, $$ω$$

The permittivity of free space, $$ε_o$$, is 8.85 x $$10^{-12}$$ F/m. The relative permittivity of a vacuum is by definition 1.

Absolute permittivity is just another name for permittivity.

Hope this helps.

• did you mean "dielectric constant is another name for relative permittivity" by the last sentence? – Enter Jul 3 '19 at 15:20
• @Enter Yes, that is my understanding. Check the following link: hyperphysics.phy-astr.gsu.edu/hbase/Tables/diel.html – Bob D Jul 3 '19 at 15:32
• as to the permittivity to be a function of frequency, did you mean the frequency of AC? – Enter Jul 3 '19 at 15:35
• Absolute permittivity of dielectric media, more often just called permittivity, is not the same as relative permittivity. – amateurAstro Jul 3 '19 at 15:53
• @Enter Yes. $ω$ is the angular frequency (radians per second) = $2πf$. Where $f$ is the AC frequency in Hz. Typically it is the static permittivity of materials tat are reported. – Bob D Jul 3 '19 at 15:55