Permittance Puns

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Exactly what the title says, I have finally got two duplicate perimeter cards, and I want to know if I should combine them now or play 100 games with them first

I know that when a light ray is incident on for example a piece of glass, the speed of light is slowed because electrons absorb and re-emit the light which has some delay, slowing the light down (I read this on libretexts, correct me if I've understood wrong). But I also know that the speed of light in a vacuum is given by 1/√(ε0μ0). What I want to understand is what the constants for permeability and permittivity in a vacuum actually mean physically. In glass and other transparent materials through which refraction can happen, it makes sense that it's just electrons reemitting light after some delay, but in a vacuum, I can't seem to understand what they are for and how they were derived.

Sorry if I've been stupid somewhere or have gaps in my understanding.

As far as I can tell, the imaginary part of permittivity is the resistance, while the real part is capacitance.

That appears to be the same as impedance, just with the real and imaginary parts switched.

What am I missing?

I'm in an undergrad electromagnetics class. My teacher is a bit non-conventional and doesn't teach from the book at all.

He has defined complex permittivity thus.

The textbook I'm using to supplement has this definition for complex permittivity.

I was watching this video on lossy dielectrics. At the given timestamp, the guy talks about two definitions for complex permittivity that are equal, but should not be combined. It appears that my teacher has combined them.

What's really going on here?

Hello,

I am trying modify a 3D FDTD electromagnetics code which would consider a tensor for permittivity.

My knowledge of FDTD was accelerated using the code found here - https://www.mathworks.com/matlabcentral/fileexchange/54557-3d-finite-different-time-domain-first-order-mur-boundary-condition

The above code would allow permittivity with different diagonal tensor components, but does not consider permittivity with off diagonal tensor components. This is all I would need to change in the code in order to introduce my results from another simulation where I have complex values of permittivity in tensor form.

Well, I may also need to consider the Courant-Friedrichs-Lewy condition as well as I'm not sure how introducing spatially varying permittivity could effect my minimum time step.

Hey all! I hope that you're having an amazing day :)

I'm currently trying to design a microstrip ring resonator. However, at some point I need to calculate the effective permittivity of some materials in order to find the ring radius. I'm just so lost, I don't even understand what is the effective permittivity or how to calculate it.

Any help/hint is welcome.

Cheers!

mean radius formula for the microstrip ring resonator

Today I got interested in the speed of light, and specifically how we can calculate it so exactly. so I did some googling, and I keep on seeing C be defined by the permittivity ε₀ and permeability μ0 of a vacuum, so I looked up those numbers, both of which are constants with the C as a factor. Doesn't the fact that both of those terms are already defined partially by C mean that its tautological to define C using those terms?

Hey All,

I'm working on a problem involving the density effect in the Bethe Bloch equation for a particle in beryllium. To get the density term I need the permittivity of beryllium but I cannot seem to find it online? If someone could point me in the right direction that would be great!

What actually is the permeability of free space and the permittivity of free space? I know it’s not super important for high school physics but I can’t let it go- I want a proper understanding of what it means rather than just throwing it into my equations because what’s the point? It’d be great if somebody could break it down for me, cheers!

Coulomb's Law $$ \vec{F} = \frac{1}{4 \pi \epsilon} \frac{q_1 q_2}{r^2} \hat{r} $$

$$ \vec{E} = \frac{1}{4 \pi \epsilon} \frac{Q}{r^2} \hat{r} $$

Let's say we want to find electric field with a distance r from charge Q. How does permittivity effects the magnitude? Will I choose the permittivity at point r or should I take into account all permittivity values between positions 0 and r?

In my opinion I should not only consider permittivity at point r but permittivities between 0 and r are effective as well. Because if we use q1 and q2 and calculate forces acting on each of them, we violate newton's third law also it is not applicable in coulomb's law. But I don't know how to calculate electric field and thus forces acting on them.

If permittivity values between 0 and r are effective on the magnitude of electric field at r, then we should be able to create a electric field isolator.

I am really confused. I hope someone can help me. Thanks in advance.

I recently learned that the dielectric constant (or relative permitivity) is not actually a constant, but it depends on wavelength or frequency (dielectric function). If that is the case, why are we taught in an introductory EM class that the dielectric constant is constant? When we say that the dielectric constant is 11.68 for silicon, which wavelength are we referring to?

When we perform a calculation that requires a knowledge of dielectric constant, which value (corresponding to which wavelength) do we use? For example, calculation of the width of space charge region requires us to know a dielectric constant of material.

w ≈ [2*ϵr*ϵ0*q*(NA+ND)/(NA*ND)*(Vbi−V)]^(1/2)

I am very confused. Please help!

I'm currently committing the cardinal sin of attempting to create a precise resonator design at 5.8 GHz using an FR4 substrate (not my idea by the way, have to for work). I ran some rough calculations and determined that I need a permittivity precision of +/- .02 to meet spec. I understand that is not even close to feasible, but what variation can I expect assuming I'm using the same manufacturer for each PCB build? I'm less concerned with the exact permittivity value and more with how much I can expect it to vary from lot to lot with the same manufacturer. Thanks!

Hello,

I am having trouble equating two concepts that I have discovered in my studies - the plasma frequency model of permittivity and the Drude model. Highly relevant here is this linked video (timestamped to the appropriate place).

In short, the slide on the video shows that the complex permittivity is given by:

epsilon_cr = epsilon_r - j * sigma / (omega * epsilon_0)

The plasma frequency model is given by:

epsilon_cr = 1 - omega_p^2 / (omega^2 + j * omega * gamma)

Where gamma is the inverse of the relaxation time.

However, when I make all of the substitutions transforming between the two models based on the slides I actually get a plus sign, not a minus sign, for the imaginary component of complex permittivity:

epsilon_cr = epsilon_r + j * sigma / (omega * epsilon_0)

And in some literature I have seen people use the above definitions with the + sign rather than -. What am I missing here? I would greatly appreciate any assistance. Thankyou.

I don't want to step on anybody's toes here, but the amount of non-dad jokes here in this subreddit really annoys me. First of all, dad jokes CAN be NSFW, it clearly says so in the sub rules. Secondly, it doesn't automatically make it a dad joke if it's from a conversation between you and your child. Most importantly, the jokes that your CHILDREN tell YOU are not dad jokes. The point of a dad joke is that it's so cheesy only a dad who's trying to be funny would make such a joke. That's it. They are stupid plays on words, lame puns and so on. There has to be a clever pun or wordplay for it to be considered a dad joke.

Again, to all the fellow dads, I apologise if I'm sounding too harsh. But I just needed to get it off my chest.

I know many consider 3-12 as childhood, and that is fine, but does not mean 2-12 is forbidden? 2-4 is preschooler because not a baby but not in school yet, 5-9 is core childhood, and 10-12 is preteen for being in double digits.

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