Polarization of an Insulator

However, due to the quantum mechanical behavior of particles, the net charge on the atom / molecule will be slightly different than it would be in an isolated state. This slight difference in charge will cause a force to be exerted on an object that is close to the atom / molecule.
  • #1

mnmman

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So I just started Physics 2 Electricity and Magnetism and I'm already scared for my life. The professor first did a demonstration where he charged up a Teflon rod on some sort of cloth and moved an aluminium can with the rod. I understand how that happens. The can is a metal and conductor so the electrons are relatively free to move around, so all the electrons go to one side of the can and the other side is positively charged so the can moved because of this polarization effect. What I did not understand was the next demonstration where he charged the same rod and moved a piece of wood (which was balanced on a pivot). I did not expect that because I thought wood was an insulator and thus the electrons are not free to move around and no polarization occurs. Can somebody explain why this happens?
 
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  • #2
What you saw was due to electrostatic induction. Despite the wood being an insulator, the molecules can still distort without any actual flow of electrons. So there will be a net surplus of electrons on the wood near a positively charged rod (polarisation) so this imbalance of charge is enough to produce a force. It's how uncharged pieces of paper and dust are attracted to a charged comb or ruler.
You need to bear in mind that there are an awful lot of electrons, on and near the surface of the insulator and when they are all displaced by a tiny distance (size of an atom) so that you can get appreciable polarisation with no flow of electrons through a substance. The dielectric between the plates of a Capacitor becomes polarised by a voltage applied across the plates - same thing happening and that increases the capacitance over what you would get with just air in between.
 
  • #3
OK so what your saying is the electrons still do move, but only within the atom or molecule?
 
  • #4
mnmman said:
OK so what your saying is the electrons still do move, but only within the atom or molecule?
To be more accurate, the charge distribution around the atom / molecule becomes distorted (polarised). In a bound state, you can't really talk in terms of electrons 'moving'.
 

What is polarization of an insulator?

Polarization of an insulator is the process in which the atoms or molecules in an insulating material become electrically polarized, meaning they develop a separation of positive and negative charges. This occurs when an external electric field is applied to the material.

How does polarization occur in an insulator?

In an insulator, the electrons are tightly bound to their respective atoms or molecules and are not able to move freely. When an external electric field is applied, the electrons are pulled slightly in the direction of the field, causing a separation of charges. This results in the insulator becoming polarized.

What is the purpose of polarization in an insulator?

The purpose of polarization in an insulator is to create an electric dipole moment, which allows the material to resist or block the flow of electric current. This is why insulators are commonly used in electrical insulation to prevent electricity from flowing through unwanted pathways.

Can the polarization of an insulator be reversed?

Yes, the polarization of an insulator can be reversed by removing the external electric field. However, the insulator may retain some residual polarization depending on the material and the strength of the field.

How does temperature affect the polarization of an insulator?

Generally, as temperature increases, the polarization of an insulator decreases. This is because at higher temperatures, the atoms or molecules in the material have more thermal energy and are able to vibrate more, making it more difficult for them to become polarized. However, this relationship may vary depending on the specific material and its properties.

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