Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why is electricity so hard to understand? (1989)

amasci.com

Post reply on HN
Print view View original

211–216 of 216 posts

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

#211

Post by roel_v »

delinka wrote: post #161
roel_v wrote: post #143

Maybe this is the right occasion to re-ask a question I asked some years ago on stack exchange, but (despite several people trying their best to explain) still failed to understand the answer to. So: does electricity have 'mass'? What I mean is, when current flows, is there a transfer of electrons (or something else) from the power source to whatever it is send to? And is there a difference between AC and DC? The con…

Yes, there is a transfer of electrons from one place to another. It's not to the thing that does work, but through the thing that does work. With a battery (DC/direct current), there's a surplus of electrons available at the negative end, a deficit at the positive end. The electrons flow through a circuit (from - to +) to perform work. With AC/alternating current, the electrons flow in one direction, then the reverse…

Right, so, in an AC circuit, there is a movement of information without a net movement of the same elektrons, right? And it's (at least partially) the same electrons that jiggle left to right, right? So is it fair to say that in a DC circuit, there is movement of mass (although net, it balances out, because what goes in out on the left comes in on the right); whereas in an AC circuit, information is transferred just through the movement of the elektrons, but not through the elektrons themselves?

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

#212

Post by roel_v »

VLM wrote: post #154
roel_v wrote: post #143

Maybe this is the right occasion to re-ask a question I asked some years ago on stack exchange, but (despite several people trying their best to explain) still failed to understand the answer to. So: does electricity have 'mass'? What I mean is, when current flows, is there a transfer of electrons (or something else) from the power source to whatever it is send to? And is there a difference between AC and DC? The con…

Information has mass. Not much. Surely charge on a dram capacitor is s bit (oh the pun) of energy and energy is mass. An excellent example of electron movement is a DC current in a metal plating tank or refining tank. Every atom of aluminum or copper or plated anything took the movement of precisely one electron (simplification because there are some non-electroplating methods for some base/plate combos, but yeah pre…

So take one RAM stick and another, with the exact same physical makeup (I know this is impossible, but for argument's sake). Now I put some information on the one, and random noise on the other. Both will have different mass, right (because there are different amounts of electrons in the capacitors of both)? Now I put valuable information on one, and I charge all capacitors of the other (so the second one has very information density, because it can be 'compressed' trivially by saying '4GB of high bits'). The second one will be 'heavier' than the first, right? And then I copy something over that second one. It's not like there is a 'transfer' of mass from the other medium to the RAM stack, because there is a net outflow of electrons, right?

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

#213

Post by tripzilch »

nilkn wrote: post #78
anu7df wrote: post #71

Earlier quoted context omitted.

I am all for introducing things the correct way, but this example of yours just does not work for me. Fractions as equivalence classes? or as a solution to an equation. No. That might work for you. In fact I might even argue that it only works for you - the child idealization created by "current you". There are many things wrong with US education. But I do not think introducing fractions using concrete examples is on…

It's fine if this wouldn't work for you. Nothing works for everyone, and that's sort of the point. Kids are funneled through an extremely rigid sequence of topics focusing entirely on rote application of manipulative techniques. Anyone who doesn't conform to this sequence is just left to painfully deal with it on their own. I remember a bit later in school I discovered algebra on my own and became really interested i…

> > If I explain 1/2 and 2/4 using pie or pizza slices and ask you how "much" pizza did you get, I think the equivalence idea clears up quite nicely.

> Sort of. But childhood me would have just told you that, no, in one case I got one big piece and in the other case I got two smaller pieces.

Why are we using pizza pies in the first place? I vaguely remember being taught something about pie as well. Instead how about this:

You have a piece of string 1 m in length. You cut it into 2 equal pieces. We can denote the length of one piece as 1/2 m.

You have a piece of string 2 m in length. You cut it into 4 equal pieces. We can denote the length of one of these pieces as 2/4 m.

These pieces of string are the same length, therefore 1/2 m is the same as 2/4 m.

Although in my head this feels more like a nice way of demonstrating they are the same, I'm not so sure if it helps a lot with reasoning about fractions. But that's fine, like the article said it's good to be able to explain something in multiple ways.

Personally that's one of the things that absolutely fascinated me about arithmetic when I was young; That you can play around and have multiple ways of arriving at the same answer, and that if you follow the rules of math right, they always end up as the same answer, sometimes even unexpectedly so (for young me).

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

#214

Post by wbeaty »

bsder wrote: post #121
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…

Carver Mead! He's one of us, ONE OF US (physics crackpots, like JG Cramer here at UW.)

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

#215

Post by nilkn »

tripzilch wrote: post #213
nilkn wrote: post #78

Earlier quoted context omitted.

It's fine if this wouldn't work for you. Nothing works for everyone, and that's sort of the point. Kids are funneled through an extremely rigid sequence of topics focusing entirely on rote application of manipulative techniques. Anyone who doesn't conform to this sequence is just left to painfully deal with it on their own. I remember a bit later in school I discovered algebra on my own and became really interested i…

> > If I explain 1/2 and 2/4 using pie or pizza slices and ask you how "much" pizza did you get, I think the equivalence idea clears up quite nicely. > Sort of. But childhood me would have just told you that, no, in one case I got one big piece and in the other case I got two smaller pieces. Why are we using pizza pies in the first place? I vaguely remember being taught something about pie as well. Instead how about…

I like your analogy a lot. It's hard to me to say definitively but I think myself as a toddler would have found it more compelling than pizza and pie analogies. Of course, the same sort of manipulation can be done with pizza/pie slices, but it's a much more natural and straightforward manipulation with strings.

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

#216

Post by wbeaty »

notalaser wrote: post #188
fzzzy wrote: post #122

Earlier quoted context omitted.

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!

Indeed. That's why I think it might have made sense back in Ampere's time. The classification of these regimes (electrostatic, magnetostatic, electrodynamic) is more recent, and Ampere's own theory of electrodynamics deals more with what we term "magnetostatic" today.

I suspect that it corresponds to Newtonian Statics, the study of mass and forces. It's a subject area; an ignoring of changes. Not a state of nonmoving. The Newtonian Statics viewpoint involves summation of forces. It may also involve taking a snapshot at one point in time.

E.g., when a mass above Earth is in free fall, it still obeys Newtonian Statics: the weight/attraction force, easily analyzed from moment to moment. The resulting acceleration and trajectory then falls under "Dynamics."

In other words, electrostatics applies to capacitors and to the mechanical forces produced by electric fields. Even if currents are also present, and even if the e-fields are changing with time, electroSTATICS still applies. (A high voltage, high-amperes power line is very "electrostatic," because of the significant e-fields and resulting phenomena.)

Static Electricity then is a chapter title, with no existence in the real world. Neither can we fill a box with Newtonian Statics. To be consistent, we wouldn't say "electrostatic motor," instead call it a capacitor-motor, or an e-field motor. (Heh, a stretched spring is statically charged! Full of Newtonian-static energy!)

Post reply on HN