Permittivity of Real Media
By convention, the electric constant ε0 appears in the relationship that defines the electric displacement field D in terms of the electric field E and classical electrical polarization density P of the medium. In general, this relationship has the form:
- .
For a linear dielectric, P is assumed to be proportional to E, but a delayed response is permitted and a spatially non-local response, so one has:
In the event that nonlocality and delay of response are not important, the result is:
where ε is the permittivity and εr the relative static permittivity. In the vacuum of classical electromagnetism, the polarization P = 0, so εr = 1 and ε = ε0.
Read more about this topic: Vacuum Permittivity
Famous quotes containing the words real and/or media:
“Somewhere along the line of development we discover who we really are, and then we make our real decision for which we are responsible. Make that decision primarily for yourself because you can never really live anyone else’s life not even your child’s. The influence you exert is through your own life and what you become yourself.”
—Eleanor Roosevelt (1884–1962)
“Today the discredit of words is very great. Most of the time the media transmit lies. In the face of an intolerable world, words appear to change very little. State power has become congenitally deaf, which is why—but the editorialists forget it—terrorists are reduced to bombs and hijacking.”
—John Berger (b. 1926)