Electric Permittivity

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cepheid
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Hi,

What is a good interpretation of electric permittivity? If you look at Coulomb's law, it seems that the electric field due to a given source charge is inversely proportional to the permittivity of the medium where the charge is located. Furthermore, the electric permittivity of a simple dielectric medium is larger than the permittivity of free space, which leads to the result that its refractive index is > 1, i.e. the higher the permittivity of the medium, the slower EM waves will propagate through it. If I'm interpreting this right, then it seems kind of counterintuitive to call the quantity "permittivity". Why isn't it called electric "restrictivity" or something like that? What am I missing?
 

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cepheid said:
Hi,

What is a good interpretation of electric permittivity? If you look at Coulomb's law, it seems that the electric field due to a given source charge is inversely proportional to the permittivity of the medium where the charge is located. Furthermore, the electric permittivity of a simple dielectric medium is larger than the permittivity of free space, which leads to the result that its refractive index is > 1, i.e. the higher the permittivity of the medium, the slower EM waves will propagate through it. If I'm interpreting this right, then it seems kind of counterintuitive to call the quantity "permittivity". Why isn't it called electric "restrictivity" or something like that? What am I missing?
You are correct in saying that permittivity of materials is higher than permittivity of free space. And yes, the higher the permittivity is the smaller the E-field will be so it seems like it should be called something like "restrictivity". I don't know why it is called permittivity...I didn't name it. Someone had to name it and came up with permittivity..I dunno.

However, it does tell us how the E-field is permitted to pass through various media...however the degree to which the material is permitted simply varies inversely with the permittivity. There's not THAT much wrong with it I guess.

Maybe someone more knowledgeable will be able to shed some insight.
 
  • #4
I think electric permitivity is a characteristic of a material to polarize when in contact with an electric or magnetic field, thus reducing the force of the field. Is that right?

Kind of like...
the electric field is the amount of money one has to distribute and the permittivity is the amount people taking that money. The more people who take the money, the less money or electric or magnetic field there is to polarize something else. If no one shows up to get any money, then that is maximum permitivity (=1) and the money passes thru unabaded just a an electric field is equal to

Electric Field =Q/permittivity. Q/1 is Q

Is this a fair analogy?
 

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