1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Is Plate Capacitor Gap a "Non-linear" Medium?

  1. Feb 14, 2018 #1
    Could the space (air gap) between two DC charged parallel plates be considered to be a "non-linear" medium with respect to an EMF radiated by a coil contained within that space?
     
  2. jcsd
  3. Feb 14, 2018 #2

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Only if the PD were very near the breakdown potential. Superposition applies over a huge range of Field Strengths and Air is more likely to be linear (in the limit) than any solid dielectric, I think.
     
  4. Feb 14, 2018 #3
    In practical HV applications, the inner surfaces of the flat capacitor plates would probably be covered in a material such as mylar or kapton sheet. As I understand its molecules would be distorted by the superposed ES field gradient.

    Would this of itself not give rise to some form of non-linearity with respect to intersecting EMF's?

    Although not germaine to the OP, it might also be pointed out that in a spherical or cylindrical cap the charge distribution itself is non-linear.

    All this no doubt becomes more complex if AC instead of DC is applied.

    Comments?
     
  5. Feb 14, 2018 #4

    Dale

    Staff: Mentor

    An ideal capacitor is linear, by definition. Any nonlinearity is a defect in the capacitor.

    Most real capacitors are pretty close to linear if operated within their designed parameters.
     
  6. Feb 14, 2018 #5
    There appears to be a difference of opinion on this since the charge/discharge curves of a cap are exponential. There is no straight line relationship between V and I unless plotted together.

    The dielectric material also needs to be factored in. Does it have ferroelectric properties?

    http://www.eecg.toronto.edu/~ali/ferro/model.html

    Here is a thought. What would happen if I sandwitched a flat spiral coil of insulated wire between two oppositely charged disks and fed it with a non-repetitive signal?

    Could such a configuration be used to simulate a ferroelectric dielectric?
     
  7. Feb 14, 2018 #6

    Dale

    Staff: Mentor

    The defining equation ##i=C\frac{d}{dt}v## is a linear differential equation. As I said above, a capacitor is linear by definition
     
  8. Feb 14, 2018 #7
    I did not mean to disagree with you, but was rather inquiring about any predictable effect upon the ideal linearity of a plate cap that might be caused by insertion within it of an EMF radiating coil.
     
  9. Feb 14, 2018 #8

    Dale

    Staff: Mentor

    Regarding that, I agree with @sophiecentaur’s assessment in post 2.
     
  10. Feb 15, 2018 #9

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I think you mean an EM radiating coil. It's not appropriate terminology to talk of radiating an EMF.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted