Why is electricity so hard to understand? (1989) • Hacker News Board

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

#171

Post by wbeaty » Wed, Nov 09, 2016, 2:14 AM UTC

bandrami wrote: post #86

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…

Intuitive but wrong (and doggedly persistent) idea #1: "electric current is moving electrons". It is moving photons, exciting (largely) stationary electrons. I can't stress how crucial overcoming that misconception was when I was doing EE.

Actually, it's electric wattage which is the moving photons, not electric current. Energy flow. Joules per second, same as with laser outputs.

So, the electric companies are selling us 60Hz photons.

But at the same time, the AC electricity just vibrates back and forth inside the wires, without any net forward motion.

About the only accurate diagram of EM spectrum I've ever encountered was the one made by R. Oppenheimer and sold as a classroom poster by The Exploratorium in SF. At the bottom, below VLF radio, we find audio-freq phone lines, and below that, 60Hz power lines. "Electric power" is on the EM spectrum, down below radio waves.

And yes, if we have a big enough antenna tower, then we can hook it up to a 60Hz dynamo, and spew 60Hz EM radiation out into space. Actually that concept was one of N. Tesla's great breakthroughs: hooking a steam-powered 50KHz alternator directly to an antenna, and broadcasting a silent carrier: CW. A couple years after his patents on this ran out, GE suddenly announced the "Alexanderson Alternator!" Finally making music/voice broadcasting possible! The public wondered how Alexanderson managed to come up with such an amazing idea. (If investors had bought Tesla stock, we'd have had AM radio ~20 years earlier. Tesla clearly grasped the concept that "radio" was the same thing as "electric power," just higher in frequency.)

https://www.datavisualization.ch/wp-content/uploads/2009/07/...

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

#172

Post by wbeaty » Wed, Nov 09, 2016, 2:18 AM UTC

mannykannot wrote: post #132

feedjoelpie wrote: post #44

Earlier quoted context omitted.

Poor selection of link. Fortunately the author saw us and pointed us toward the articles instead of the raw notes: http://amasci.com/miscon/whyhard1.html#def

I am not sure that is a big improvement. I dipped in here, and what I found was mostly a repetitive litany of complaints.

The entire essay-collection is a critique of grade-school electricity textbook chapters, in the USA. (I don't know if the texts in other countries are promoting the same misconceptions.) To avoid reading critiques/corrections, go to any other site except mine. Also see:

Am I just a pedantic nitpicker?

http://amasci.com/miscon/nitpik.html

To deeply grasp physics, often one must UN-learn the common misconceptions which were acquired in our early school careers. The misconceptions in this list are the ones believed by educators, and taught to students.

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

#173

Post by tropo » Wed, Nov 09, 2016, 2:39 AM UTC

glandium wrote: post #135

tropo wrote: post #109

Earlier quoted context omitted.

Similar problem from a local school: "__ - 9 = 9" The teacher would accept 9 or 0 as an answer, not 18. A parent (with math degree even) who was volunteering pointed out that 18 is correct. The teacher ruled against this, arguing that 18 was unacceptable because math with 2-digit numbers hadn't been covered yet. This was at a "good" school, in a county full of nerds. Such logic. Poor kids... and people wonder why kid…

How do they justify 0 or 9 as an answer? 9 - 9 is not 9, neither is 0 - 9.

Yeah...

I suppose the "logic" is that stuff involving 9 could connect up with stuff involving 0 or 9. Since all other 1-digit answers seem more distantly related, and the answer has to be 1-digit because 2-digit hasn't been covered, 0 and 9 are the most attractive answers and therefore correct. ???

Remember, that was a class with smart kids in a school in a good area. Imagine what it might be like in not-so-good areas or in the classes that aren't for smart kids.

People who truly hate math are teaching. My sister-in-law is an example. She got a "degree" in "early childhood education". It's a joke. The hardest math she had to pass was algebra, as is taught in 7th grade. Boy did she complain about that class. She thought it was really hard to pass algebra. I'm horrified she got more than halfway through high school without it, yet there she was, taking it in college.

Teachers have serious credential inflation. Many have Master's degrees... but are those degrees worth anything?

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

#174

Post by andars » Wed, Nov 09, 2016, 2:46 AM UTC

dom0 wrote: post #147

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…

+1 It took me a huge amount of time to get rid of all the BS learned in school. In some area I'm even still working on it (eg. analysis).

When you say analysis, do you mean you are working on unlearning the stuff you learned in it, or learning it to replace something else?

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

#175

Post by snarfy » Wed, Nov 09, 2016, 2:51 AM UTC

I actually like the water model. Here is a transistor:

http://imgur.com/a/vhrmR

It breaks down as an analogy as soon as magnetic fields come in to play, which is pretty much any AC circuit.

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

#176

Post by mohaine » Wed, Nov 09, 2016, 3:39 AM UTC

slavik81 wrote: post #136

Asooka wrote: post #97

Earlier quoted context omitted.

Children take a long time to realise that one half of pizza is the same as two quarters. In general you can give a child less pizza and as long as it's the same number of pieces, they can't tell the difference. The well-known experiment is with presenting two sets of pieces of chocolate, one with less chocolate but more pieces and most children say the one with more pieces has more chocolate.

I'm not sure I believe this. My experience with children is that they're almost always smarter than I expected. I think I've found the Wikipedia article about the effect, and the criticisms section [1] matches my bias, in that it suggests the children are confused because they are thinking not just about the material presented to them, but also why they're being asked. [1] https://en.wikipedia.org/wiki/Conservation_(…

Depends on what you mean by children. Most of these concepts appear as a child ages but I think they get out of the simple ones pretty early.

I know before a certain developmental state children will say a taller thin glass holds more then a short wide glass even if you pour them back and forth to show they are equivalent. Once they "get" the concept it is for life but before that it is impossible, logic be dammed.

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

#177

Post by crador » Wed, Nov 09, 2016, 3:46 AM UTC

seiferteric wrote: post #49

justifier wrote: post #35

Earlier quoted context omitted.

From the linked notes: I never really understood capacitors until I started trying to construct proper water-analogies for them. Then I discovered that my electronics and physics classes had sent me down a dead-end path with their garbage about "capacitors store electric charge." Since my discovery, I've gained significantly more expertise in circuit design, which leads me to a sad thought. Maybe the more skilled of…

Not really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) int…

Capacitors do store energy, in their electric field. Potential energy in general, as far as I'm aware, is stored in fields of some sort -- water turning a wheel (gravitational), tension in a spring (electromagnetic), capacitors (electromagnetic), chemical energy in gasoline (electromagnetic), nuclear energy (weak/strong fields I believe, not as well versed here) and so forth.

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

#178

Post by wbeaty » Wed, Nov 09, 2016, 3:52 AM UTC

bandrami wrote: post #117

pitaj wrote: post #107

Earlier quoted context omitted.

Ehhhhh. Not really. It is the rate of charge passing through a cross-section. That's how it's defined, and as an EE student, what you're saying made little-to-no sense to me.

And the boson that mediates "charge" is....?

Note that photons only travel along FO cable because of the charge polarization of the silica. This is a direct analog to 60Hz "electric power" traveling along a column of mobile charges in a long conductor. In both cases, the electrons wiggle back and forth, while the photons couple to them, and are guided along. But charge is not energy, in exactly the same way that amperes are not watts, and current is not EM energy-flow. Coulombs wiggle within the waveguide, while the Joules proceed continuously forward as propagating waves.

The EM energy is in the form of propagating waves, while electric charge provides the medium: the waveguide.

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

#179

Post by crador » Wed, Nov 09, 2016, 3:53 AM UTC

justifier wrote: post #64

seiferteric wrote: post #49

Earlier quoted context omitted.

Not really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) int…

i agree, I linked more for the similarity in experience between the gp and the author in regard their unlearning I prefer your clarifications when considering the function of capacitors That said, water does attract water.. the term used to describe the phenomena is cohesion https://en.m.wikipedia.org/wiki/Cohesion_(chemistry)

Don't forget about gravity as well.

Interestingly, cohesion itself is caused by electric fields between water molecules due to their polarity (uneven distribution of charge, oxygen is electron-greedy). Much like a capacitor, separating the molecules (plates of the capacitor in the analogy) requires work which gets stored in the electric field between them.

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

#180

Post by crador » Wed, Nov 09, 2016, 4:07 AM UTC

k__ wrote: post #24

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 got it taught about 3 or 4 times, and every time I understood it less. In middle school they told me, it's electrons moving at the speed of light through a conductor. In high school they told me, no no, they don't move at the speed of light, just when one electron enters the conductor, another one on the other side will leave the conductor, like with peas in a straw. And this enter/leaf is at the speed of light. At…

Let's start with a familiar example. The speed of sound is basically fixed, and signals caused by perturbing air molecules will propagate with this speed. This is true regardless of the gross wind conditions at play -- the speed of sound is much greater than the propagation speed of any single air molecule.

Similarly the speed of light is fixed, and is really the speed of propagation of electomagnetic waves. When you perturb electrons, other electrons will react to that change in the fields as it arrives at them with the speed of light. So even though the flow of electrons down the wire is very slow, the flow of energy or information may be very fast. In fact, you don't need electrons in between to move at all -- you can simply have empty space in between your antenna and the electrons you are moving around ;).

As it happens, these electromagnetic waves have components that stand orthogonal to eachother. If you take relativity into account, you can find a frame of reference where the magnetic field disappears -- really the magnetic field is just a relativistic correction of the electric field and explains why charged particles attract eachother differently when moving versus at rest. In any case, it is really just one field that is called electromagnetic because we used to think it was two completely separate fields!