6 ms·

How electricity doesn't work

53 points by xbryanx 17y ago

RK 17y ago
With something like this it's hard to tell if the author is "dumbing it down" or just doesn't understand the material all that well. He does style himself an "amateur physicist".
kurtosis 17y ago
This is quite discouraging to read - the author sets out to correct many common misconceptions but ends up introducing many more - (e.g. electrons don't "hop" from atom to atom (there are some quite useful models of metals based on hopping), metals bend because electrons "fill in" the gaps) Reading this reminds me of the importance of mathematics for placing a hard edge on vague and potentially confusing terms like "flow" "current" "energy" "store" etc. etc. I wonder if it is possible to give 6th graders correct intuition about electricity without math?
- wbeaty 16y ago
  >This is quite discouraging to read... It's quite discouraging to see criticism from someone who didn't read what they're attacking. The article plainly states that electrons in metals are hopping all the time, even when the current is zero. Go read it. That's the whole point of that section. A bit hard to miss, unless you leapt to a wrong conclusion after only reading the title. > because electrons "fill in" the gaps The article specifically describes this effect. It's probably not wise to criticize things you haven't bothered to read. That section is a simplified introduction to the concept of "electron sea" and "drift velocity." It debunks the common grade-school textbook error that electrons in metal wires only start hopping between atoms if someone connects that wire in a battery circuit (where the electrons also are supposed to remain stuck to individual metal atoms when current is zero.) This is a serious textbook misconception because it teaches kids that the electron sea doesn't exist, and it prevents them from grasping the "full pipes" fluid analogy of electric circuits as well as later concepts of metallic bond, metal reflectivity, lack of brittleness, etc.
- argv_empty 17y ago
  Why without math?
  - henning 17y ago
    Correctly describing electromagnetics involves invoking vector calculus, which is a tall order for 10 year old children even in education systems more rigorous than America's.
    - DaniFong 17y ago
      You don't need vector calculus. My demonstration of the power factor is a children's swing: if you push against your friend as they travel out you do work on them: if you make contact with your friend aas they're coming back, they do work on you. Kids have a pretty good mechanical model of swing sets.
      - vitaminj 17y ago
        Do kids actually learn about power factor? That point aside, while an intuitive understanding is nice, power factor is really a mathematical construct arising from the multiplication of two out-of-phase sinusoids (i.e. voltage and current). I think to really understand active / reactive power and pf, you need to look at the maths. It's really not that difficult. And you certainly don't need to know vector calculus, merely high school trig.
    - argv_empty 17y ago
      Fully describing it, yes, but a 6th grader should at least be able to handle Ohm's law >_>
    - afterburner 17y ago
      What about pictures and animations of those vectors? They don't have to perform operations on those vectors to start understanding, they just have to see the vectors. In other words, they have to see pictures of arrows.
- onoj 17y ago
  Are the models of metals /hopping you are referring to involving free outer electrons in a metal crystal lattice - as he was referring to?
  - kurtosis 17y ago
    Yeah - especially metals like Fe, Co, and Ni where the conduction electrons are derived from the atom's d-orbitals. The hopping is one of the key elements of the "hubbard" model. This viewpoint doesn't add very much if you want to calculate the conductivity or optical properties, but it is essential for understanding the magnetism of these materials. What bugged me about this article was that without doing a quantitative analysis of a model and comparing it's predictions to experiments - physical interpretations like whether the electrons are hopping or not are so ambiguous that they are effectively meaningless.
- lutorm 17y ago
  I would argue that correct intuition about anything can be had without math. Using math may be one way of gaining that intuition, but intuition, by its very nature, is not mathematical. I'm not sure it's useful to argue whether an intuitive picture of electrons hopping or not is more correct. (Electrons are in any case not really little balls that are in one place.) These are all models of the world made with specific goals, where the most "correct" model would be solving the schrodinger equation for a macroscopic system -- something that would not give you any particular insight as to how things behave. I think the usefulness of an intuitive layman's understanding should be derived from whether it makes you conclude the correct things about the macroscopic behavior of electricity.
Dunearhp 17y ago
He confuses his own internal mental model with the actual nature of electricity. Mostly this is just arguments about semantics.
tbrownaw 17y ago
Really that entire site is wonderful, and quite varied. But note that it's largely not solid reference material (aside from perhaps portions of the electricity stuff), it's more fun and interesting things to play with / think about, that often require some knowledge of science to understand or make work or show why they can't work. And a little bit of crackpottery, some of which is even explicitly labeled as such.
derefr 17y ago
Disregarding the content of this work (the author's conception of electricity, or lack thereof), I found this passage in the preface to be striking: > After my encounter with those books, I slowly realized that my own understanding of basic electricity was flawed and incomplete. I sat down and started re-teaching myself the subject. I became aware of the source of my problem: I myself had learned a bunch of electricity misconceptions as a child. Those early misconceptions gave me a faulty foundation on which to build further knowledge. As a result, any accurate information learned later became distorted in my mind even as I learned it. If the foundation is distorted, then the "building" cannot be built. It was like trying to build a brick wall on top of a garbage pile: the incoming bricks are perfectly good, but they simply did not fit upon earlier concepts, and any structures that I managed to build kept collapsing. Many of the textbooks he was reading through (K-6 level books) were using the pedagogical technique of http://en.wikipedia.org/wiki/Lie-to-children http://en.wikipedia.org/wiki/Lie-to-children , where one purposefully gives inaccurate-but-simple information, planning to supplant it later with more accurate accounts once a foundational knowledge of the terms and laws of the system have been built within the student's mind. Both the misconceptions he is addressing, and his own misconceptions, show that this technique is more dangerous than it is believed to be, because people keep these inaccurate accounts, resisting learning the more complex but real accounts due to some bastardized version of Occam's razor.
- wbeaty 16y ago
  > Many of the textbooks he was reading... were using the pedagogical technique of Lie-to-children Wrong, the textbook authors fully believe those misconceptions themselves. I discovered this sad fact during my K6 education consulting work back in the 80s. Lies-to-children are very different than author misconceptions: they must be carefully constructed so that they don't install permanent major misconceptions in student's minds. For example, the idea that atoms are like tiny solar systems is a "Lie" which simply explains atomic structure in classical terms, and which turns out to be relatively harmless. It doesn't form any enormous learning barrier which entirely derails our later ability to understand orbitals and quantum chem. Good articles on the author-misconception topic: R. Feynman's "Judging books by their covers" and S J Gould's "The case of the creeping fox terrier clone"
- 17y ago
Daniel_Newby 17y ago
Not accurate. Among many problems, when electrons move, they do tend to move near the speed of light. (The low rest mass means that even tiny amounts of kinetic energy really get them zooming along.) However in Ohmic conductors they frequently crash into scatterers, bouncing off at a random angle and imparting heat to the material. In everyday materials like copper at room temperature, they spend so much time bouncing around that the average velocity of a conduction electron is low. EDIT: If you want to teach electricity, describe it as a fluid acted on by fast-moving pressure waves. Resistance can be reasonably described by analogy to a viscous fluid flowing through a sponge.
- Confusion 17y ago
  I figured he was going to explain how (free) electrons (at room temperature, in a metal) actually move around at around 0.5c, but alas.
petercooper 17y ago
As with electricity, the average person is also taught how fixed wings provide lift incorrectly: http://en.wikipedia.org/wiki/Lift_(force)#.22Popular.22_explanation_based_on_equal_transit-time http://en.wikipedia.org/wiki/Lift_(force)#.22Popular.22_expl... - I've come across plenty of smart people (though with no formal physics knowledge) who blindly believed the transit time theory.

53 points by xbryanx 17y ago

RK 17y ago

With something like this it's hard to tell if the author is "dumbing it down" or just doesn't understand the material all that well. He does style himself an "amateur physicist".

kurtosis 17y ago

This is quite discouraging to read - the author sets out to correct many common misconceptions but ends up introducing many more - (e.g. electrons don't "hop" from atom to atom (there are some quite useful models of metals based on hopping), metals bend because electrons "fill in" the gaps) Reading this reminds me of the importance of mathematics for placing a hard edge on vague and potentially confusing terms like "flow" "current" "energy" "store" etc. etc. I wonder if it is possible to give 6th graders correct intuition about electricity without math?

wbeaty 16y ago
>This is quite discouraging to read... It's quite discouraging to see criticism from someone who didn't read what they're attacking. The article plainly states that electrons in metals are hopping all the time, even when the current is zero. Go read it. That's the whole point of that section. A bit hard to miss, unless you leapt to a wrong conclusion after only reading the title. > because electrons "fill in" the gaps The article specifically describes this effect. It's probably not wise to criticize things you haven't bothered to read. That section is a simplified introduction to the concept of "electron sea" and "drift velocity." It debunks the common grade-school textbook error that electrons in metal wires only start hopping between atoms if someone connects that wire in a battery circuit (where the electrons also are supposed to remain stuck to individual metal atoms when current is zero.) This is a serious textbook misconception because it teaches kids that the electron sea doesn't exist, and it prevents them from grasping the "full pipes" fluid analogy of electric circuits as well as later concepts of metallic bond, metal reflectivity, lack of brittleness, etc.
argv_empty 17y ago
Why without math?
- henning 17y ago
  Correctly describing electromagnetics involves invoking vector calculus, which is a tall order for 10 year old children even in education systems more rigorous than America's.
  - DaniFong 17y ago
    You don't need vector calculus. My demonstration of the power factor is a children's swing: if you push against your friend as they travel out you do work on them: if you make contact with your friend aas they're coming back, they do work on you. Kids have a pretty good mechanical model of swing sets.
    - vitaminj 17y ago
      Do kids actually learn about power factor? That point aside, while an intuitive understanding is nice, power factor is really a mathematical construct arising from the multiplication of two out-of-phase sinusoids (i.e. voltage and current). I think to really understand active / reactive power and pf, you need to look at the maths. It's really not that difficult. And you certainly don't need to know vector calculus, merely high school trig.
  - argv_empty 17y ago
    Fully describing it, yes, but a 6th grader should at least be able to handle Ohm's law >_>
  - afterburner 17y ago
    What about pictures and animations of those vectors? They don't have to perform operations on those vectors to start understanding, they just have to see the vectors. In other words, they have to see pictures of arrows.
onoj 17y ago
Are the models of metals /hopping you are referring to involving free outer electrons in a metal crystal lattice - as he was referring to?
- kurtosis 17y ago
  Yeah - especially metals like Fe, Co, and Ni where the conduction electrons are derived from the atom's d-orbitals. The hopping is one of the key elements of the "hubbard" model. This viewpoint doesn't add very much if you want to calculate the conductivity or optical properties, but it is essential for understanding the magnetism of these materials. What bugged me about this article was that without doing a quantitative analysis of a model and comparing it's predictions to experiments - physical interpretations like whether the electrons are hopping or not are so ambiguous that they are effectively meaningless.
lutorm 17y ago
I would argue that correct intuition about anything can be had without math. Using math may be one way of gaining that intuition, but intuition, by its very nature, is not mathematical. I'm not sure it's useful to argue whether an intuitive picture of electrons hopping or not is more correct. (Electrons are in any case not really little balls that are in one place.) These are all models of the world made with specific goals, where the most "correct" model would be solving the schrodinger equation for a macroscopic system -- something that would not give you any particular insight as to how things behave. I think the usefulness of an intuitive layman's understanding should be derived from whether it makes you conclude the correct things about the macroscopic behavior of electricity.

Dunearhp 17y ago

He confuses his own internal mental model with the actual nature of electricity. Mostly this is just arguments about semantics.

tbrownaw 17y ago

Really that entire site is wonderful, and quite varied. But note that it's largely not solid reference material (aside from perhaps portions of the electricity stuff), it's more fun and interesting things to play with / think about, that often require some knowledge of science to understand or make work or show why they can't work. And a little bit of crackpottery, some of which is even explicitly labeled as such.

derefr 17y ago

Disregarding the content of this work (the author's conception of electricity, or lack thereof), I found this passage in the preface to be striking: > After my encounter with those books, I slowly realized that my own understanding of basic electricity was flawed and incomplete. I sat down and started re-teaching myself the subject. I became aware of the source of my problem: I myself had learned a bunch of electricity misconceptions as a child. Those early misconceptions gave me a faulty foundation on which to build further knowledge. As a result, any accurate information learned later became distorted in my mind even as I learned it. If the foundation is distorted, then the "building" cannot be built. It was like trying to build a brick wall on top of a garbage pile: the incoming bricks are perfectly good, but they simply did not fit upon earlier concepts, and any structures that I managed to build kept collapsing. Many of the textbooks he was reading through (K-6 level books) were using the pedagogical technique of http://en.wikipedia.org/wiki/Lie-to-children http://en.wikipedia.org/wiki/Lie-to-children , where one purposefully gives inaccurate-but-simple information, planning to supplant it later with more accurate accounts once a foundational knowledge of the terms and laws of the system have been built within the student's mind. Both the misconceptions he is addressing, and his own misconceptions, show that this technique is more dangerous than it is believed to be, because people keep these inaccurate accounts, resisting learning the more complex but real accounts due to some bastardized version of Occam's razor.

wbeaty 16y ago
> Many of the textbooks he was reading... were using the pedagogical technique of Lie-to-children Wrong, the textbook authors fully believe those misconceptions themselves. I discovered this sad fact during my K6 education consulting work back in the 80s. Lies-to-children are very different than author misconceptions: they must be carefully constructed so that they don't install permanent major misconceptions in student's minds. For example, the idea that atoms are like tiny solar systems is a "Lie" which simply explains atomic structure in classical terms, and which turns out to be relatively harmless. It doesn't form any enormous learning barrier which entirely derails our later ability to understand orbitals and quantum chem. Good articles on the author-misconception topic: R. Feynman's "Judging books by their covers" and S J Gould's "The case of the creeping fox terrier clone"
17y ago

Daniel_Newby 17y ago

Not accurate. Among many problems, when electrons move, they do tend to move near the speed of light. (The low rest mass means that even tiny amounts of kinetic energy really get them zooming along.) However in Ohmic conductors they frequently crash into scatterers, bouncing off at a random angle and imparting heat to the material. In everyday materials like copper at room temperature, they spend so much time bouncing around that the average velocity of a conduction electron is low. EDIT: If you want to teach electricity, describe it as a fluid acted on by fast-moving pressure waves. Resistance can be reasonably described by analogy to a viscous fluid flowing through a sponge.

Confusion 17y ago
I figured he was going to explain how (free) electrons (at room temperature, in a metal) actually move around at around 0.5c, but alas.

petercooper 17y ago

As with electricity, the average person is also taught how fixed wings provide lift incorrectly: http://en.wikipedia.org/wiki/Lift_(force)#.22Popular.22_explanation_based_on_equal_transit-time http://en.wikipedia.org/wiki/Lift_(force)#.22Popular.22_expl... - I've come across plenty of smart people (though with no formal physics knowledge) who blindly believed the transit time theory.