Relative permittivity Puns

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!

Also, as I understand, capacitance is εA/d, where ε is the absolute permittivity. If the capacitor's dimensions are kept constant, then a change in ε with frequency should mean a change in capacitance (?). So why do they say capacitance isn't affected by frequency (but rather capacitive reactance)?

There is this question where relative permittivity varies linearly with distance from one capacitor plate to the other. Then we are supposed to calculate effective capacitance, given variables- Area of the capacitor plates - a Distance between the plates - d Permittivity of free space - E Relative Permittivity at one plate- Er1 Relative Permittivity at the opposite plate- Er2

The formula for this is- C = (Ea(Er2 - Er1))/(d ln(Er2/Er1) )

Now can someone please help me with the derivation...

Been working on a project that involves a liquid level sensor. During my research I found myself wondering what portion of the capacitance equation is changing when liquid levels change on a partially submerged parallel plate capacitor.

I am referring to this form of the equation:

Capacitance = (relative permittivity)* (permittivity of space) * (Plates area) / (distance between plates)

Here's a visual to show off what I am trying to explain: https://zippy.gfycat.com/SnarlingWarpedGuillemot.webm

Relative permittivity is what I am thinking because the dielectric is changing. If this is the case, how do I go about knowing relative permittivity at any given liquid level?

Concrete dry 4.5

https://en.wikipedia.org/wiki/Relative_permittivity

Ground Penetrating Radar, Volume 1 edited by David J. Daniels, page 90:

>concrete dry 4 - 10 permittivity 2 - 12 attenuation dBm

>concrete wet 10 - 20 permittivity 10 - 25 attenuation dBm

https://books.google.com/books?id=16PV-fhKasoC&pg=PA90&lpg=PA90&dq=shale+attenuates+radar&source=bl&ots=u_5FRpT1sd&sig=21kh_y-Ms7SkZqNePk7s74WhoZY&hl=en&sa=X&ved=0ahUKEwjX45DKseTVAhVKslQKHRuqA544ChDoAQg1MAQ#v=onepage&q=shale%20attenuates%20radar&f=false

Dielectric Properties of Portland Cement at Low Radio Frequencies (1995)

https://www.academia.edu/4216490

I cannot find the permittivity of hematite and magnetite. Their dielectric constants are listed in Table 1 on page 118:

>Hematite over 80

>Magnetite over 33.7, under 81

http://www.minsocam.org/ammin/AM21/AM21_115.pdf

I cannot find the permittivity of magnetite concrete or hematite concrete.

Please dumb it down, I just can't wrap my head around the topic Thanks

I am modeling joule heating from a DC current on an object in Comsol v4.3, and apparently it needs to know the relative permittivity of the materials it is made of, although this is blank in the materials library.

After some Googling, I've found out that it's very hard to find the relative permittivity of metals, and some people are saying it should be zero and others are saying it should be infinity. Apparently it's properly an imaginary number any way.

Anyone know what value I should put in, or where I could find it? any input at all would be appreciated!

From 'Table 4.3 Attenuation and Relative Dialectric Constant of various materials measured at 100 MHz' from Ground Penetrating Radar, Volume 1 edited by David J. Daniels, page 90

https://books.google.com/books?id=16PV-fhKasoC&pg=PA90&lpg=PA90&dq=shale+attenuates+radar&source=bl&ots=u_5FRpT1sd&sig=21kh_y-Ms7SkZqNePk7s74WhoZY&hl=en&sa=X&ved=0ahUKEwjX45DKseTVAhVKslQKHRuqA544ChDoAQg1MAQ#v=onepage&q=shale%20attenuates%20radar&f=false

Difference in attenuation between sea water and fresh water

'Table 4.3 Attenuation and Relative Dialectric Constant of various materials measured at 100 MHz' from Ground Penetrating Radar, Volume 1 edited by David J. Daniels, page 90

Attenuation, dB

Fresh water 0.01

Freshwater ice 0.1 - 2

Sea water 100

Sea water ice 1 - 30

https://books.google.com/books?id=16PV-fhKasoC&pg=PA90&lpg=PA90&dq=shale+attenuates+radar&source=bl&ots=u_5FRpT1sd&sig=21kh_y-Ms7SkZqNePk7s74WhoZY&hl=en&sa=X&ved=0ahUKEwjX45DKseTVAhVKslQKHRuqA544ChDoAQg1MAQ#v=onepage&q=shale%20attenuates%20radar&f=false

My comment

Fresh water and sea water have by far the highest relative permittivity. This explains why immersing one's body in fresh water or sea water is by far the best shielding. Even better than clay and oil.

This also explains why wearing wet clothes shields radar.

This also explains why containers of sea water attenuate better than containers of fresh water. Shielding reports are in the Shielding: Water wiki in /r/targetedenergyweapons.

https://www.reddit.com/r/TargetedEnergyWeapons/comments/5i5t6z/wiki_shielding_water_attenuates_emf_elf_and/

I know the equation that relates the three constants: c=(ε0*µ0)^-(1/2) However, I never understood why this worked or if there was a conceptual reasoning behind it, so any explanation would be greatly appreciated.

I find good answers like http://pleclair.ua.edu/impedance/The%20Relationship%20Between%20Loss.pdf for the case that there is a omega!=0 (equation 11), but what about the trivial (?) steady state?

Background: I want to calculate the E-field of two electrodes in the presence of two media - marine water and sediment and a metal conductor. Both water and sediment have specific permittivity and conductivity, and those would both have an influence on how the electic field is formed. A schematic drawing is here: https://docs.google.com/drawings/d/1Dp184YrxuvFd2CXGur9X5QcOJuYlBREZsxztJ7IrrhI/edit?usp=sharing I facilitate electical mirror charges to calculate the electric potential field, neglecting the conductivity, and get reasonable results, but I need help with bringing the conductivity into the equation. you can find my calculations here: https://cocalc.com/share/f7766c5e-2f4d-4916-bb0d-74a7182e5fd5/E-Feld-2019-03-12-114056.sagews?viewer=share

Today in my Electromagnetic fields and waves exam i had a problem that is given

Relative permittivity = 2 Relative permeability =1

Coaxial transmission line has capacitance = 1nF.

Find the inductance of the cable?

Can anyone help?

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.

Title may be a bit odd so here is the story. Moved here from Iceland at 16-17 in 2013, had a hard time in school as I wasn't learning the language well as this was not planned and I did not want to move so no excited preparation on Duolingo (was that even a thing yet?). About 4 years in or so of bad grades and poor attendance in Teknologi og industrifag (2 years) and IKT (1 year) and a starting year to help learn the language (which did not go well as it assumed I had already had a basic grasp which I did not) I was advised to just try and get a job through NAV which I did and and now it's been 4 years and change and I've gotten much much better at the language (still lots to learn though) and would like to return to school in 2022 or 2023 at the latest but I'm not how to go about it as I am 25 right now which I seem to recall having read is the max age for VGS at least for free (?). I'm not sure if I'm able, what I should study (recommendations are welcome) as IKT was sort of something I wanted to do but I struggled greatly with keeping up as I had to constantly translate most everything I read and lectures flew over my head every time, it was embarrassing every time we were given an assignment and everyone got right on to it but I always had to ask the teacher to help me get going. But I think I still would like to study something tech related.

The last couple of years have not been kind, I had finally gotten a real proper job (not through NAV) at Gardermoen in late 2019 and that ended within 6 months cause Covid and I apparently didn't qualify for permittering money as I had not worked long enough as I understood it (my boss thought it was unfair as well but was powerless to help). Now it's 2 years later of nothing, no education not work (despite trying, I have a T1-4 truck license) and am sick of it. Thank fully I do have a family here that supports me so I'm not out on my ass but this is no life. Perhaps went in too much detail here but I just want to express that I am not in a good place and need any and all advice I can receive cause I am lost in my life in a country I don't fully understand and going back to Iceland is not an option right now. Thank you for reading.

Do your worst!

They were cooked in Greece.

I'm surprised it hasn't decade.

Don't you know a good pun is its own reword?

Two muffins are in an oven, one muffin looks at the other and says "is it just me, or is it hot in here?"

Then the other muffin says "AHH, TALKING MUFFIN!!!"

For context I'm a Refuse Driver (Garbage man) & today I was on food waste. After I'd tipped I was checking the wagon for any defects when I spotted a lone pea balanced on the lifts.

I said "hey look, an escaPEA"

No one near me but it didn't half make me laugh for a good hour or so!

Edit: I can't believe how much this has blown up. Thank you everyone I've had a blast reading through the replies 😂

It really does, I swear!

Because she wanted to see the task manager.

But that’s comparing apples to oranges

Heard they've been doing some shady business.

but then I remembered it was ground this morning.

Edit: Thank you guys for the awards, they're much nicer than the cardboard sleeve I've been using and reassures me that my jokes aren't stale

Edit 2: I have already been made aware that Men In Black 3 has told a version of this joke before. If the joke is not new to you, please enjoy any of the single origin puns in the comments

BamBOO!

They’re on standbi

A play on words.

My daughter, Chewbecca, not so much.

Pilot on me!!

Christopher Walken

Nothing, he was gladiator.

Or would that be too forward thinking?