Non-polar dielectric in electric field

[andyupnorth]

I'm searching for a dielectric material that does not get attracted to the +ve or -ve plates of an electric field.

 

Could someone correct me if this is wrong, but does a non-polar dielectric (e.g. pressurized SF6) get attracted to a positive or negative plate? Or does it simply attenuate the electric field without having a force induced in it since it does not get polarized?

 

Furthermore, IF a non-polar dielectric is not attracted to an electric field source, THEN what non-polar material/gas out there has the highest dielectric constant (i.e. relative static permittivity)?

[granpa]

in a uniform field a dielectric will not be electrostatically attracted or repelled.

[andyupnorth]

Thanks for the quick reply.

 

So a non-polar or polar material has nothing to do with attraction or repulsion from the field source?

 

And what about charges getting accumulated on the surface of the dielectric from the source (which, say, is a few centimeters away across air)? Won't that charge buildup cause repulsion from the source?

[granpa]

the dielectric is neutral overall. if the field is uniform then the positive and negative charges cancel and there is no net electrostatic force.

[andyupnorth]

Granpa, I strangely got the exact opposite answer from a different forum:

 

--> http://www.sciforums.com/showthread.php?t=93508

 

Or are you guys actually agreeing but talking about two different aspects?

 

Very confusing!

 

P.s. How do we decide which forum to battle this out in?

[CaptainPanic]

I'm no expert, but if I remember the formula to calculate the force in an electric field well, then the particle must have a (net) charge. If it has no charge, then there is no force.

 

A polar particle might align its internal charges with the field.

 

I'm awaiting our experts to give feedback.

 

And we're fighting this out in this forum, whether you like it or not.

[swansont]

The material will become polarized; in a uniform field, the force on the + and - charge of the dipole will be equal. That causes the orientation, but there is no net force on the material. +qE - qE = 0

 

I think the attraction mentioned in that other post was referring to the orientation of the dipoles, rather than the bulk behavior.

[andyupnorth]

So is it the surface charge on the dielectric that pulls or pushes the dielectric in a non-uniform field? If so, can't we just ground the dielectric? (assuming part of it is far away from the electric field)

 

Besides, were does the surface charge come from anyway?

[granpa]

the surface charge on a dielectric comes from the same place that it comes from in a conductor. the shift of the electrons to one side of the material. if the shift is uniform then the charges cancel everywhere except the sufrace. in a dielectric the shift is limited because the electrons are bound to their individual nuclei (they dont shift very far). for this same reason grounding it will have no effect.

 

in a non-uniform field you will also have 'bound charge' (different but related meaning) in the interior of the material. bound and surface charges are responsible for the net force.

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Merged post follows:

Consecutive posts merged

http://www.physicsforums.com/showthread.php?t=78954

Edited June 9, 2009 by granpa
Consecutive posts merged.

[andyupnorth]

Thanks. You've been most helpful.

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Merged post follows:

Consecutive posts merged

Sorry for beating the subject to death, but...

 

So a non-polar dielectric like pressurized SF6 (dielectric constant ~7) cannot get polarized, right?

[granpa]

why couldnt it?

[swansont]

It wouldn't feel a net force, but that's not the same as saying it wouldn't become polarized. That's what happens to a dielectric — the dipoles align to partially cancel the field.

[andyupnorth]

So if we stop thinking about the term "dielectric", is there a way for a material to not get attracted to neither the +ve or -ve plates of an electrostatic field source, yet this material attenuates an electric field going through it?

[swansont]

So if we stop thinking about the term "dielectric", is there a way for a material to not get attracted to neither the +ve or -ve plates of an electrostatic field source, yet this material attenuates an electric field going through it?

 

 

Already answered — yes.

[nathan3011]

I'm glad that i found this thread i had one of the queries but you guys ahve already answered it for me

 

Thank you for this