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Relative Permittivity

by Ancho
Tags: permittivity, relative
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Oct25-13, 10:51 PM
P: 1
Hello forum members,

I am trying to wrap my head around the concept of relative permittivity. I have read the Wikipedia article on the subject, but I don't feel quite satisfied. As far as I understand it, RP is essentially a measure of how well a given material holds a static charge relative to a vacuum, which makes it similar to conductance, resistivity and dielectric strength, no? If not, how exactly is it related to those concepts?

Another thing I don't quite understand is how RP relates to capacitance. For instance, let's say I have two small, geometrically identical spheres with a 10cm diameter. According to the calculations from wolfram alpha, each sphere will have a self-capacitance of 5.563 picofarads, but these calculations don't take into account the nature of the material of the spheres. What if one is made of a material with a very high permittivity, like 10,000, while the other is made of a material with a permittivity of 10? Would that not change the capacitance values of the spheres quite drastically?

The whole subject feels like soup in my head at the moment . Help with clearing up these concepts would be highly appreciated.
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Oct26-13, 01:00 AM
HW Helper
P: 5,356
Hi Ancho.

Permittivity is not related to dielectric strength or resistivity. Think of a parallel plate capacitor, with a vacuum or dry air gap between the plates. If you fill the air gap with a material having relative permittivity of 4, then the capacitance (the number of charges the plates store for a given potential difference) goes up by that same factor of 4.

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