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Why is electricity so hard to understand? (1989)

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Re: Why is electricity so hard to understand? (1989)

#121

Post by bsder »

bronlund wrote: post #6

In fact, it isn't so hard that they would like you to believe - it just seems that way when they remove the best parts due to national security :D You would have to go back to James Clerk Maxwell's original 20 equations to see what it's all about. Okey, quaternions are kind of hard, I'll admit to that, but all in all it makes much more sense.

> You would have to go back to James Clerk Maxwell's original 20 equations to see what it's all about. Okey, quaternions are kind of hard, I'll admit to that, but all in all it makes much more sense.

Not ... really. The problem is that we teach electromagnetics using a 19th century pedagogy that assumes the existence of the Ether.

This works well for some things and makes them nicely closed form and simple. Of course, it breaks down for other things (motors are one of the big ones) where you really want a field description.

Of course, a field description makes nothing simple and closed form. So, it isn't good for making exams out of.

If you can deal with 4-vectors, "Collective Electrodynamics" is a really good book.

Re: Why is electricity so hard to understand? (1989)

#122

Post by fzzzy »

notalaser wrote: post #115
fzzzy wrote: post #100

Earlier quoted context omitted.

I'm not sure they are terrible. Electrostatic describes charges at rest, capable of inducing a voltage across a dielectric. Electrodynamic describes charges in motion, capable of inducing a current across a conductor. They seem like apt descriptions to me.

It doesn't sound too bad when you put it that way, and it certainly made sense back when Ampere introduced the term, but: * It doesn't match the way we define electrostatics, magnetostatics and electrodynamics. What defines electrodynamics isn't the fact that charges are moving (they're moving if the currents are constant, too, but the magnetic fields produced by steady currents are in magnetostatics' yard) but the i…

Thanks for writing that out! Very interesting.

I guess it all comes down to the fact that a magnetic field does not exist without an electric current. One way of thinking about it sees it as charges moving, and the other way of thinking about it sees it as a static magnetic field.

I guess that's why the terms are archaic!

Re: Why is electricity so hard to understand? (1989)

#123

Post by gugagore »

CamperBob2 wrote: post #116
gohrt wrote: post #79

Earlier quoted context omitted.

It's hardly fair to say that water analogies are good but "capacitors store charge" is bad, they are both weak analogies

There's nothing weak about saying capacitors store charge. That's exactly what they do. You measure charge in coulombs, which is how you count electrons. Capacitance is just the value that relates stored coulombs of charge to available voltage.

I didn't agree with what you wrote and maybe I can explain why. Springs store inches. You measure displacement in inches. Spring constant is just the value that relates stored inches to available force.

(You can swap roles of force and displacement if you wish, the point is the same. It sounds bad to say springs store force or displacement, to me.)

Re: Why is electricity so hard to understand? (1989)

#125

Post by [deleted] »

CamperBob2 wrote: post #116
gohrt wrote: post #79

Earlier quoted context omitted.

It's hardly fair to say that water analogies are good but "capacitors store charge" is bad, they are both weak analogies

There's nothing weak about saying capacitors store charge. That's exactly what they do. You measure charge in coulombs, which is how you count electrons. Capacitance is just the value that relates stored coulombs of charge to available voltage.

[deleted]

Re: Why is electricity so hard to understand? (1989)

#126

Post by [deleted] »

CamperBob2 wrote: post #116
gohrt wrote: post #79

Earlier quoted context omitted.

It's hardly fair to say that water analogies are good but "capacitors store charge" is bad, they are both weak analogies

There's nothing weak about saying capacitors store charge. That's exactly what they do. You measure charge in coulombs, which is how you count electrons. Capacitance is just the value that relates stored coulombs of charge to available voltage.

[deleted]

Re: Why is electricity so hard to understand? (1989)

#127

Post by CamperBob2 »

gugagore wrote: post #123
CamperBob2 wrote: post #116

Earlier quoted context omitted.

There's nothing weak about saying capacitors store charge. That's exactly what they do. You measure charge in coulombs, which is how you count electrons. Capacitance is just the value that relates stored coulombs of charge to available voltage.

I didn't agree with what you wrote and maybe I can explain why. Springs store inches. You measure displacement in inches. Spring constant is just the value that relates stored inches to available force. (You can swap roles of force and displacement if you wish, the point is the same. It sounds bad to say springs store force or displacement, to me.)

But inches are an abstract measurement of distance. Electrons are a thing.

(Well, depending on who you ask... no one has ever seen one, and some people have claimed half-jokingly there's only one electron in the entire universe: https://en.wikipedia.org/wiki/One-electron_universe .)

Re: Why is electricity so hard to understand? (1989)

#128

Post by farright »

Like incompressible fluids, electricity is hard to reason about because we work in a limit that does not obey local causality.

The entire system must be solved simultaneously, and there is not a well defined "input" or "output". This can be seen from the fact that when we analyze a circuit we also include the model the power source and the load.

The combination of non-locality and complex boundary conditions makes it hard to apply ordinary intuition. We would like to say that the power source "does something" to the circuit but causality actually runs both ways. E.g. if we have a constant voltage source, then the circuit will determine how much current flows through the source. If we have a constant resistance load, then the load will determine how much power the circuit applies to it.

Re: Why is electricity so hard to understand? (1989)

#129

Post by ihaveahadron »

notalaser wrote: post #16

I think more than half the time I spent earning my EE degree has been spent unlearning the intuitive (but wrong) things that I was liberally taught. I was fortunate enough to have an exceptional Physics teacher in high school, who managed to avoid a lot of the bullshit that less fortunate students were fed; sadly, I compensated that with some of my own (misguided) self-study. This experience also taught me to activel…

I had to unlearn a shitload of made up crap that I was told. I also had to invent a lot of shit. Then I was able to get a glimpse into reality.

Re: Why is electricity so hard to understand? (1989)

#130

Post by [deleted] »

soneca wrote: post #38

It looks like interesting content, but I got a little confused by the writing style and general layout. A more succinct, clearly defined structure would help me a lot. Each topic could be clearer on what is wrong and how is the right way. It would help a lot just to start with a clear: "What is the right definition of the word electricity?". Then, maybe a "What is "electrical phenomena" and some examples". "Correct d…

[deleted]
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