Electrostatics
Kicking off electromagnetism with electrostatics — what static electricity actually *is*, why charges sit still, and diving straight into Coulomb's law!
Hello~ ~ I’m going to start posting about electromagnetism too….
It’s because of this that I’ve developed the habit of studying every single day;;
Gosh, when I do this, I write drafts on A4 paper, you know?…
Right now I’ve organized about 50~60 pages….;;;
Ahhh……when am I going to post all this????lol lol lol
Anyway, I’ll get started.
Electromagnetism starts with electrostatics (electro-sta-tics).
Meaning we’ll be dealing with static electricity.
Honestly, back in middle school and high school physics class when we learned about electricity, ‘static electricity’—what is that -_-?
When you say static electricity, rubbing a notebook cover on your clothes and putting it near your hair to make the hair stand up,
or when you grab a doorknob, etc. etc. etc.
“Aaack@!@#!@$#$!!!!”
saying you got zapped by static.. that’s the only thing that came to mind, so
“What on earth IS static electricity -.-!!!!!!!!” I remember thinking that.
So what is static electricity
Um…first, let me say this is how we view the meaning of the word. The opposite of static electricity is dynamic electricity(?).
Static electricity is the situation where charges are locked in place, not moving!!!!! Conversely, dynamic electricity is when the charges are moving
If you put some charge on a conducting sphere (metal ball), what happens?
Because of the repulsive forces between them, the charges will zoom zoom zoom out to the very outer surface, right?
When charges are moving like this, it’s not static electricity~ okey dokey??????
We’re not going to deal with this kind of thing yet
(It gets briefly covered at the very end of Electromagnetism II, and it’s freaking hard. But even that is only a very shallow level, I think. Anyway, dynamic electricity is super freaking hard……lol)
We’re going to investigate the state after these charges have distributed themselves all the way out and are now at rest, or at some moment! at that mo~~ment!! or alternatively
the state where Megaton Superman is holding them perfectly still so they can’t move? That’s what we’re exploring hehe
Let’s start from Coulomb’s law.
Coulomb’s law (Coulonb’s law) Fixed point charge q, a test charge Q separated by a distance—what force does it receive???
(η: rather than writing it as eta, we use “relative r” (relative distance), and the notation
is written in English cursive r, but there’s no way to write English cursive r on the blog;;; so I decided to use eta, which looks the most similar.)
Why is the magnitude of the force like this???? “I dunno!!!” Call God up and ask Him
«In some class a professor said this. In science you have to understand what comes first. It’s not “because of this, therefore that~ ah I see~~~”
Nature comes first. Humans who looked at that Nature went “oho? How does this work??” and then came to realize, ah, that’s how it is»
Anyway, Coulomb’s law is also just that Coulomb, the guy, did experiments and found it to be this way hehe
(The superposition principle that’s about to come out is the same.
It’s not that it naturally follows the superposition principle!! It’s that when they experimented, that’s what they found. Look at it a certain way, doesn’t the superposition principle seem way too obvious???
No, No, No!!!! It’s not. If the force had been proportional to the square of the variable, it wouldn’t follow the superposition principle)
Alright and in there
is the permittivity of ‘vacuum’ (permittativity of free space).
Imagine doing this experiment.
The force due to charges! Doesn’t it seem like the ’electric force’ would show up differently in vacuum, in air, and in water?
Somehow??a bit?
And when they checked it with experiments, that’s what they found. So this proportionality constant was introduced.
(Probably in high school we just thought of 1-over-four-pi-epsilon-zero as all one proportionality constant and learned it lumped together as k?????lol I’m not a high schooler so I won’t use k..T_T)
Now what if there’s more than 1 point charge??? Let’s say there are n of them. (Now you’ll understand why we used eta.)
The test charge Q, due to each of the point charges q1, q2, q3, q4, q5……. qn, will receive Coulomb forces
from each one ~. These force vectors all add up and will act as if they were a single force.
«The reason I wrapped that last red-underlined part in square brackets one extra time for no reason is to explain the electric field E!!!!»
The electric field created at some position by some set of charges!!!
When you think about this electric field, you don’t need the test charge Q, right??
What is an electric field (electric filed)? Honestly, I don’t really know what electricity is either.
If I had to put the above expression into words, “the influence that charges create and exert on charges. That kind of space(?)”
If we think about it in connection with gravity.
In some book I saw gravity described as a warping of spacetime?
Um, if you put a bowling ball on a Simmons mattress,
the ping-pong balls, golf balls, etc. around it would roll and fall toward the bowling ball, right?
The bowling ball is the sun, and the ping-pong ball is the earth.
And if we say this gravitational ‘field’ is the influence that an object with mass creates and exerts on another object with mass, that kind of space(?), doesn’t it click more easily?
My writing skills are lacking so I don’t think I described it well…. If anyone has ideas…please let me know…hehehe
Please leave a comment~ hehehe
This post has too much rambling, so I’ll wrap it up at the Coulomb force.
From the next post I’ll go go with more substantial content hehehe
Gotta start writing right away
Originally written in Korean on my Naver blog (2014-11). Translated to English for gdpark.blog.