Electrostatic field question

Sure. Just like a piece of coaxial cable, the dielectric constant or permittivity will change the characteristic impedance and propagation delay.

Or, if you like, the material will change the capacitance between them.

boB

Sorry that does help me understand. This is goes back to the two insulated plate electrodes with an emulsion between them. I want to know, if I introduce a plastic sleeve over part or all of of one of the electrodes, do I still have the same V/cm treating my emulsion? Thanks, Mikek

No.

.

Joe Gwinn

Hmm, I think that helped. At least now, I realize my emulsion dielectric constant is 50 ± and any plastic I would use, has a much lower dielectric constant and is much thinner. I think the effect will be a non issue. Thanks for the input, Mikek

It depends on the relative dielectric constants of the plastic and of the emulsion. If the plastic Kd is lower, the field gradient in the emulsion will decrease.

What's the dielectric constant of the emulsion? I'd expect it to be pretty high. Water is 78, and most plastics will be single digits.

If the emulsion is conductive, which it probably is, adding plastic will further decrease the field in the emulsion. Maybe drastically.

Yes, kinda. The volts dropped in the plastic can be different from the (gas, liquid) fill, if the dielectric constants mismatch. In the extreme case of very high dielectric constant, it's the same as changing a metal electrode diameter. In the extreme case of very low dielectric constant, it's a match for vacuum.

OK, I see I think.

If the dielectric is between the two concentrics, then it will change things. But if it is around the whole thing, then not so much.

Does that sound right ?

boB

Well, no; the issue is that the dielectric has (resistive and capacitive) conductivity, and is in series with the (resistive and capacitive) conductivity of the emulsion. It's a voltage divider, with a voltage ratio that depends on the unknown emulsion as much as the (presumably known) dielectric. The "V/cm" measure, though, can remain constant, if the emulsion and dielectric are matching materials; you've changed both the "V" and the "cm" parts by displacing emulsion with the dielectric.

That is a description that I understand. I seems like a non problem, I have good test results at

800V/cm to 3000V/cm and can go higher if needed. There is also the possibility that lower voltage are viable. Thanks, Mikek

You electrically get the same result as putting a capacitor in series with the electrodes and making them slightly larger except that now there's no metal touching the emulsion.

This is what I was trying to say but the illistration is better.

I don't think the OP actually described what he wanted to know as good as he could have.

Inserting a dielectric of greater than 1 (e_0) between the plates or tubes in this case will increase the capacitance.

boB

The dielectric must be an electric insulator so R should be very high for that substance. Like, glass or ceramic.

The dielectric will increase the capacitance if its permittivity is greater than 1 relative to air, given the same distance between those

2 conductive tubes.

boB