B What is the Physical Meaning of Permittivity of Free Space?

[gracy]

What actually is permittivity of free space I know it is εo and I know it's value but I want to know it's physical meaning,what does it actually do ?I have referred this
https://www.physicsforums.com/threads/what-is-permittivity.763156/#post-4804922
but did not get the answer.
I have also watched this video

 

[Dale]

It is simply a SI unit conversion factor between Newtons, meters, and Coulombs. It does not even exist in other unit systems, like Gaussian units.

 

[gracy]

what it does?

 

[Dale]

It converts units of Coulombs to units of Newton's and meters.

 

[gracy]

It converts units of Coulombs to units of Newton's and meters.

how?

 

[Dale]

$1\;C^2=4\pi \epsilon_0 \;N m^2$

 

[gracy]

But I thought it is something abut allowing electric field to enter in a region.

 

[Dale]

It is just a unit conversion factor, and only in SI units. In Gaussian units charge is defined in terms of the dyne and cm such that there is no similar conversion factor.

You may be thinking about the permittivity of a material, but free space is not a material.

 

[gracy]

Ok what is permittivity of material?

 

[Dale]

I think you already have a separate thread on that. It is not a good idea to have two open threads discussing the same topic. Let's keep this thread for vacuum questions and the other thread for material questions.

 

[gracy]

But that thread was about susceptibility not permittivity.

 

[Dale]

$\epsilon = (1+X_e) \epsilon_0$

 

[gracy]

Ok, susceptibility and permittivity are related but not the same thing.

 

[Dale]

More importantly, vacuum and material are not the same thing.

 

[gracy]

yes.

 

[gracy]

What each term indicates in your equation?
$ε$= permittivity of a material
εo=permittivity of free space/vaccum

χe =susceptibility of ?

 

[cnh1995]

What actually is permittivity of free space I know it is εo and I know it's value but I want to know it's physical meaning,what does it actually do ?

According to my understanding, permittivity is a measure of charge required to create an electric field in a dielectric. It is not the physical definition but certainly helped me understand its applications.

 

[cnh1995]

χe =susceptibility of ?

The material..

 

[cnh1995]

In this video example, a slab of conducting material is placed in vacuum and subjected to an electric field E. Due to this field, there will be rearrangement of the charges on the slab surfaces to make the field inside the slab 0. Due to rearrangement, there will be charge densities created on opposite faces. Now, this charge density will be of the lowest possible value in case of vacuum(ε_o is the lowest). If this slab were placed in water(higher ε), the charge density required(or allowed) to create the same electric field E would be higher (ε_r times).
This is the principle used in the capacitors.

 

[gleem]

Susceptibility is a measure of the ease with which a material may be polarized defined by the equation

P = ε₀χE

with χ = K -1 K being the dielectric constant of the material and the permittivity ε = (1 + χ)ε₀

Thus permittivity is a measure of how a material affects an electric field by its presence. since

D = εE since D is the electric field due to free charges and E is the net field in the presence of a dielectric.

 

[Dale]

OK, it looks like the discussion on the permittivity of free space is done, and now we are discussing permittivity/susceptibility of a material. Further such comments can go to the other thread:

https://www.physicsforums.com/threads/dielectric-polarisation.846822/#post-5311771

This one will be closed to keep things sane.