Grokking electricity

After I finished an electromagnetism course in college, I said that one day I’d go back and really understand the subject. Now I’m starting to do that. I want to understand theory and practical applications, from Maxwell’s equations to Radio Shack.

I’m starting by reading the Feynman lectures on E&M. After that I plan to read something on electronics. If you have resources you recommend, please let me know.

I’ve started new Twitter account, @GrokEM. I figure that tweeting about E&M will help me stick to my goal. My other Twitter accounts post on a regular schedule (plus a few extras) and are scheduled weeks in advance. GrokEM will be more erratic, at least for now. (In case you’re not familiar with grok, it’s a slang for knowing something thoroughly and intuitively.)

[Update: GrokEM has become ScienceTip and is about more than E&M.]

Here’s what Feynman said about mathematicians learning physics, particularly E&M.

Mathematicians, or people who have very mathematical minds, are often led astray when “studying” physics because they loose sight of the physics. They say: “Look, these differential equations — the Maxwell equations — are all there is to electrodynamics … if I understand them mathematically inside out, I will understand the physics inside out.” Only it doesn’t work that way. … They fail because the actual physical situations in the real world are so complicated that it is necessary to have a much broader understanding of the equations. … A physical understanding is a completely unmathematical, imprecise, and inexact thing, but absolutely necessary for a physicist.

Heinlein coined grok around the same time that Feynman made the above remarks. Otherwise, Feynman might have said that only studying differential equations is not the way to grok electrodynamics.

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17 thoughts on “Grokking electricity

  1. Unfortunately, Radio Shack isn’t what it used to be. Now there are either no electronic components at all, or you can’t get to the few that are left without someone trying to sell you a cell phone.

  2. Yes, your average neighborhood Radio Shack is not the mecca for components and amateur electronics advice it once was. The maker movement, however, is a much likelier source of people doing great stuff with electricity. While Wired has been covering it forever, even Forbes recently added a blog on it. That and the ability to order cheap components from around the world on the Internet have revolutionized the home study of Electricity. Oh, and just be careful not to order multiples of lithium batteries, smoke detectors, or model rocket engines!

  3. I had a similar experience to what Feynman spoke to in the paragraph above. I started as a Math major and took up Physics in my sophomore year. I had the same prejudice of “if it’s an equation, then I fully understand it.” It took me a year to figure out that I needed to really work on developing a physics intuition if I was going to really get what was going on. It was a humbling and beneficial experience.

    I just had a similar experience to what you are doing with going back to E&M… I recently went back and wanted to understand precession in a gyroscope from a forces perspective, rather than the conservation of angular momentum argument. When introducing the conservation of angular momentum, the gyroscope is the first example that is looked at, and is used to show why it is a powerful tool. The standard argument uses torque vectors, which, though correct, isn’t physically intuitive to me because they are not real, physical things, but rather an accounting tool to keep track of forces. So I tried to resolve the forces to see why procession happened, and it was damn tricky. I have an old physics friend who is now a physics prof who worked on it with me, and we both struggled. He brought it to the department, and they struggled. Finally, he was able to pull up a bunch of old papers on the subject from the 50s and 60s, and one of them had a decent layout of the accounting of physical forces and why they induced procession, but even following the vectors and forces in that paper was non-trivial.

    I think it is good to go back and grok what you initially learned, and, with experience, ask yourself if you really understood it to begin with. In the case of the gyroscope, I thought I understood what was going on because I just accepted the angular momentum equations, and didn’t look into what intuitions regarding forces that angular momentum replaces. Now I have an appreciation for what sort of magic you get from it, why it is so helpful, and how the physical force model meshes with the angular momentum one a bit better.

  4. I second the “Art of Electronics” recommendation. That book alone will get you well on your way when it comes to actually using electricity for practical purposes.

  5. As a text on the more theoretical aspects of E&M, I strongly recommend Griffith’s Introduction to Electrodynamics. It’s the best physics textbook I’ve ever read, with clear, deep explanations, a large trove of interesting problems and many references to accessible recent literature.

  6. I’ve been a practicing EE for longer than I care to think about. But it’s been a lot of fun.

    I agree with the recommendation of the Horowitz and Hill book. But also let me recommend the lecture notes from R. D. Middlebrook, formerly of CalTech. Sadly Middlebrook died in 2010, but his lecture notes are still available. See his web-site, .

    One comment regarding differential equations in electronics: As applied, they generally assume linearity. This is only a loose approximation at best, especially when active gain elements (transistors, etc.) are included in the mix. And for large signal situations, the approximation can break down rather badly.

    You will need to “play” with actual circuits to gain any real understanding.

    And E&M is a whole ‘nother ball game. In free space Maxwell is relatively straight forward. But when you add ferrous material, the boundary conditions and the non-linearities of the ferrous materials can make life “interesting”.

    Remember, “the only way to eat an elephant is one bite at a time”. So take it in small chunks and keep chewing.

  7. I am coming from almost the opposite direction (strong intuition of electronics, little understanding of the math), but asked my guru. His take:

    1) LaPlace and Fourier transforms make life simpler and avoid some issues with Diff. Eqns.

    2) Seconds Horowitz and Hill.

    3) Highly recommends the lecture notes from R.D. Middlebrook’s Cal Tech seminar:

    4) You need to “play” with actual circuits to make headway.

  8. There is a danger, I think, in failing to see the perspectives from which people come to things. Physicists love and need simplicity and ultimate forms. They are capable, and many experimental physicists, especially, are among the cleverest people I have ever met, and have amazing breadths of understanding. Still, their motive is to simplify.

    The engineer wants to get stuff done, and learning about limit cases and edge cases is part of their business. These are annoying to physicists. In illustration, go find and read what Feynman wrote about tribology.

    It’s not that one field has a “deeper” understanding than the other. They have a different perspective. Chemistry cannot really be “reduced” to physics because, finally, of computational limits. Thus, chemistry exists as an independent field. I’d say engineering has a fine future for itself in that kind of realm. Just remember, engineers are splitters, too: The kinds of things you can do when communicating among points within the ocean are vastly different than are available in air or space.

    Despite the power and pride of ab initio methods, there isn’t much in science and engineering that can be done that way. It’s quite often necessary to work from observed or experimental data, interpreted with physical models.

    Despite all this, it’s amazing to me how far you can get with relatively simple methods.

  9. I also recommend Griffith’s Introduction to Electrodynamics. His explanations are simple and clear.

  10. i second griffiths’ introduction to e&m.

    and as for tweeting to stick to goals, you might find beeminder of interest as an alternative commitment device. (stay on the yellow brick road, or pay the price :))

  11. I’ve always liked The Mechanical Universe videos on the history of physics, now available online.
    For electromagnetism, start on #28 Static Electricity

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