TBR dielectric constant

[capn jazz]

---

Members don't see this ad.

So I'm in the Electrostatics chapter of TBR Physics. The entire 2-page dielectric constant section is COMPLETELY baffling me. It's pages 116-117 of book 2 of physics. I thought I understood the description of it, but the two example questions make NO SENSE. Like the explanation confuses me endlessly. Can someone easily relate the following terms for me/explain those 2 pages in easier terms?

dielectric constant
polarizability
ionization

Thanks!

 

[Dr Gerrard]

Don't have TBR, so sorry if there is any confusion.

Anyways, I don't know this material the best either, but here is a shot.

A dielectric is an insulator which is placed between the capacitor plates and resists the creation of the electric field. Since it resists the electric field, the capacitor holds more charge in order to resist this resistance? haha. So, a dielectric constant is a value given to the dielectric, with air having one of a little greater than one, and a vacuum having a value of 1.
Putting a dielectric increases the charge, keeps the potential the same, and thus increases the capacitance. This can be seen by both C = Q/V and C = K*eA/d, where K is the dielectric constant and e is epsilon-naught, some permittivity constant.

A dielectric works through polarization. The polarization of the medium, or the dielectric, is what causes the electric field in the opposite direction.

Finally, dielectrics are chosen such that they are resistant to ionization, because ionization will cause flow between the two plates, which is not wanted.

Sources:

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/dielec.html
http://en.wikipedia.org/wiki/Dielectric

 

[ChexMix]

Sorry to bring this thread back, but I was reading TBR physics and had the exact same question. and I found this thread after a search.

In TBR, the paragraph on dielectric constant is pretty vague, it says

"Dielectric behaviour results from a medium's polar nature. A strongly polar medium responds to an external electric field by reorienting its polar molecules, so that the net electric field within the medium becomes weaker than the external field. Such a field strength reduction diminishes the interactive forces between all charges within the medium."

I guess I am confused as to what this external field is (I thought the field is inside the medium), and how the net electric field is reduced (by reorienting the medium's molecules or the charges that was creating the electric field)?
Also, from reading the online explanations, they seem to refer to dielectric as something nonpolar (or insulating) that is placed in between a capacitor. Does that have anything to do with the dielectric constant we are talking about here? Here we seem to say that the dielectric behaviour results from polar medium (the more polar the higher the dielectric constant and weaker the electric field/force in that medium)

If anyone would help me out on this, I would really appreciate it! 🙂
And Capn Jazz did you ever find out about your question?

 

[G1SG2]

Sorry to bring this thread back, but I was reading TBR physics and had the exact same question. and I found this thread after a search.

In TBR, the paragraph on dielectric constant is pretty vague, it says

"Dielectric behaviour results from a medium's polar nature. A strongly polar medium responds to an external electric field by reorienting its polar molecules, so that the net electric field within the medium becomes weaker than the external field. Such a field strength reduction diminishes the interactive forces between all charges within the medium."

I guess I am confused as to what this external field is (I thought the field is inside the medium), and how the net electric field is reduced (by reorienting the medium's molecules or the charges that was creating the electric field)?
Also, from reading the online explanations, they seem to refer to dielectric as something nonpolar (or insulating) that is placed in between a capacitor. Does that have anything to do with the dielectric constant we are talking about here? Here we seem to say that the dielectric behaviour results from polar medium (the more polar the higher the dielectric constant and weaker the electric field/force in that medium)

If anyone would help me out on this, I would really appreciate it! 🙂
And Capn Jazz did you ever find out about your question?

This is from TPR:

"The electric field between the plates will polarize the molecules and will create tiny dipole moments in the molecules of the insulator. These layers of induced charge on the opposite surfaces of the dielectric are the source of a new electric field through the dielectric, Einduced, a field that points in the opposite direction from the E field created by the charged capacitor plates themselves (because E fields always point from positive and toward negative source charges). Einduced points in the direction opposite to E, so the net field strength is reduced to E-Einduced."

So basically, the electric field polarizes the molecules of the dielectric which causes dipole moments. These induced charges create a new electric field, but because it points in the direction opposite to that of the original field, the net field is reduced (E-Einduced). Hope that helps.