How electricity doesn't work

by xbryanx • 16 years ago

53 21 16 years ago

kurtosis2• 16 years 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?

argv_empty2• 16 years ago

Why without math?

henning• 16 years 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.

onoj• 16 years 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?

kurtosis2• 16 years 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.

lutorm2• 16 years 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.

wbeaty2• 16 years 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.

RK• 16 years 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".

Dunearhp• 16 years ago

He confuses his own internal mental model with the actual nature of electricity.

Mostly this is just arguments about semantics.

tbrownaw• 16 years 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.

derefr2• 16 years 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 , 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.

lutorm2• 16 years ago

I'm not sure what you are arguing here. What would a world look like without simplification? You want people to remain in complete ignorance until they are judged at some point to be "ready" to learn the complete truth about something? That seems like an absurd viewpoint to me.

Besides, your comment ignores the fact that people, in the absence of explanations (right or wrong) will make up their own model of how things work. That model is just as hard to unlearn as an incorrect view they may have been taught by an instructor. In fact, they are probably harder to unlearn because they are based on the persons own experiences.

All learning involves correcting and building on earlier concepts, there are no "tabula rasa". What is important is that people confront and integrate their own preconceptions as part of learning.

The National Academies Press book "How People Learn: Brain, Mind, Experience, and School" is a good, accessible introduction to these concepts. It's on the web at http://www.nap.edu/html/howpeople1/.

This is a relevant passage: "A logical extension of the view that new knowledge must be constructed from existing knowledge is that teachers need to pay attention to the incomplete understandings, the false beliefs, and the naive renditions of concepts that learners bring with them to a given subject. Teachers then need to build on these ideas in ways that help each student achieve a more mature understanding. If students' initial ideas and beliefs are ignored, the understandings that they develop can be very different from what the teacher intends."

derefr2• 16 years ago

I'm not arguing that we should not simplify instruction at lower levels; I'm simply arguing that there are ways to simplify without creating inaccuracies: to avoid using leaky analogies, for instance.

wbeaty2• 16 years 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"

Daniel_Newby• 16 years 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• 16 years 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• 16 years 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_expl... - I've come across plenty of smart people (though with no formal physics knowledge) who blindly believed the transit time theory.

How electricity doesn't work

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