How do the charges in a glass set up their own counterbalancing electric field when an electric field from external source is imposed on glass?

[King E]

Let’s start out with a glass with no electric field in it. Now we we impose an electric field on the glass by sending light in it. Then, how do the charges in the glass set up their own counterbalancing electric field in opposite direction that results in reducing the total electric field?

 

 

Edited April 11, 2022 by King E

[swansont]

Dipoles in the material will align with the electric field

[King E]

17 hours ago, swansont said:

Dipoles in the material will align with the electric field

??

[exchemist]

28 minutes ago, King E said:

??

You are not providing much context to your enquiry, and this response of yours is similarly not one to which an informative response can be made.

If you could explain in more detail what phenomenon you are trying to understand, we can help you further. As it is, all I can usefully say is that glass is polarisable, due to the electrons in its chemical bonds (the valence electrons). 

[swansont]

1 hour ago, King E said:

??

Some materials are polar - they have a charge distribution, even though they are neutral. There's no net effect if they are randomly oriented, but in a field, they tend to align. And most atoms will become dipoles (induced dipole) in the presence of an electric field. This charge distribution will affect the net electric field inside a material.

https://en.wikipedia.org/wiki/Electric_dipole_moment

[exchemist]

46 minutes ago, swansont said:

Some materials are polar - they have a charge distribution, even though they are neutral. There's no net effect if they are randomly oriented, but in a field, they tend to align. And most atoms will become dipoles (induced dipole) in the presence of an electric field. This charge distribution will affect the net electric field inside a material.

https://en.wikipedia.org/wiki/Electric_dipole_moment

Yes. In the case of the polarisation in glass induced by EM radiation, we have to be talking about induced dipoles, i.e. in the electron distribution. One would not want to give the impression that light is able to alter the arrangement of the Si (δ+) and O (δ-) atoms in the crystal structure.

But I do feel it would help to know what the context is for the poster's question. It could be to do with reflection, or with refractive index, or perhaps something else.  

  

[King E]

1 hour ago, exchemist said:

Yes. In the case of the polarisation in glass induced by EM radiation, we have to be talking about induced dipoles, i.e. in the electron distribution. One would not want to give the impression that light is able to alter the arrangement of the Si (δ+) and O (δ-) atoms in the crystal structure.

But I do feel it would help to know what the context is for the poster's question. It could be to do with reflection, or with refractive index, or perhaps something else.  

  

It was about epsilon, in case of refraction.

Edited April 12, 2022 by King E
Typo

[exchemist]

9 minutes ago, King E said:

It was about epsilon, in case of refraction.

You mean ε as in the formula for refractive index n=√(εᵣμᵣ) ?

What happens is that the bonding electrons couple to the radiation, which can be thought of as a sort of forced resonance oscillation, in which the forcing is due to the oscillating electric vector of the radiation. This has the effect of changing the phase velocity of the light. It is a result of the material being polarisable by the light.  

The degree to which this occurs depends on the frequency of the light, making the refractive index different for different frequencies of radiation. This is what is called "dispersion" and is why a prism (or a raindrop) can split white light into the colours of the rainbow.

What is interesting to me, from the point of view of physical chemistry, is that the polarisability and the change in phase velocity become greater and greater, as the frequency gets closer and closer to an absorption frequency for the material. At the absorption frequency itself, you have the limiting case, in which the material becomes effectively infinitely polarisable, the phase velocity becomes zero - and the material is then opaque and absorbs the light.

In the case of silica (glass) there is an absorption band is in the UV, which occurs where the electrons in the Si-O bonds jump to a different, higher energy, molecular orbital. (There is another absorption band in the IR, which is due to excitation of a collective mode of vibration of the bonds in the crystal structure.)

So what is happening with refraction is that the light undergoes a kind of temporary pseudo-absorption and re-emission process as it passes through. It is not a real absorption however. It's more as if the light finds itself walking on a spongy, bouncy trampoline, which slows it down. (The real model for this process requires a lot of QM maths involving perturbation theory, which I once knew at university but have long since forgotten.) 

[studiot]

22 hours ago, King E said:

Let’s start out with a glass with no electric field in it. Now we we impose an electric field on the glass by sending light in it. Then, how do the charges in the glass set up their own counterbalancing electric field in opposite direction that results in reducing the total electric field?

 

 

You have demonstrated quite deep thinking about how thing work in several of your threads, rather than just accepting simplified models that you have been offered.

I did wonder if your question was prompted by having been given the usual very short explanation about dipoles aligning.
People often imagine the atoms and molecules with fixed magnets or dipoles and wonder how these can turn to alignment when the atom or molecule is fixed in space in a solid type material.

In order to understand this we need to realise that nothing physical actually turns, when the electric field is applied.
What happens is the electrion cloud changes shape.

If you would like to pursue this here is the beginning for a single atom.

 

In the absence of an external field the electron cloud is distributed evenly about the (outer parts of) the atom.
This is a time averaged evenness and may be regarded as either an even density or that the electron spends on average the same amount of time at each point.
I have tried to show this by making the shading as even as I can.

When an external electric field is applied the electrons experience an attraction to the more positive end of the field.
This increases the density on the + side and decreases it on the - side, or if you prefer increases the time the electron spends on the + side and decreases it on the - side.

This immediately generates a small field opposing the externally applied one and the atom is now polarised.

 

This simple idea can be developed a long way towards explaining the effects for molecules and much more.

 

Do you wish to continue ?