July 19, 2013 at 11:40 PM by Dr. Drang
Katie Floyd asked me an embarrassing question this morning:
@drdrang explain iPad/iPhone chargers -what controls speed of charge?, watts or Amps? Is a 2.1a 5w charger 1/2 the “speed” of a 2.1a 10w?
— Katie (@KatieFloyd) Fri Jul 19 2013 7:20 AM CDT
I fumbled out an answer that was essentially correct, but only because the question was so simple—and I still felt the need to tell her not to trust me. Electricity is, and has always been, my great blind spot. Yes, I know the elementary equations like [V = I R] and [P = I V]. If held at gunpoint, I probably could even give a reasonable rendition of Kirchhoff’s Laws.1 But that doesn’t mean I understand electricity; it just means I haven’t forgotten everything from physics class.
As long as I’m in a confessional mood, I’ll add that whenever I do need to think about electricity, I immediately shift to an analogy of water flowing through pipes, a topic I understand. It works reasonably well as a coping mechanism, but it’s pathetic.
It’s not that I think I’m intellectually incapable of understanding electricity. I just didn’t study it when I was younger and don’t have the time or inclination to do so now. And my ignorance has left scars. When I took the EIT test2 during my senior year, one of the problems was to calculate the internal resistance of a battery. I knew perfectly well that this was a simple problem that could be solved in a minute and that all the EE majors had gone right to it to ease into the test and settle their nerves. I sat there for what seemed like forever, trying to decide whether I should give it a shot, but ultimately I just didn’t feel confident enough. I switched to a problem involving, funnily enough, a water distribution system—a problem that would take a page of calculation but which was in my comfort zone. That was in 1981, and I remember it like it happened yesterday.
Even if I’d been able to answer the battery question on the EIT correctly, it would’ve said nothing about my electrical expertise. Real expertise isn’t demonstrated by spouting a few technical terms or formulas; it comes from a deep understanding of what those terms mean and when those formulas should and shouldn’t be applied.
This is, by the way, the main reason I love In Our Time. Unlike most programs of its type, it has as its guests actual experts in the topic being discussed. Other shows—Fresh Air, let’s say—typically have guests who are professional writers. These writers have spent some number of months researching a topic, usually through interviewing and the work of real experts, and then Terry Gross interviews them. Melvin Bragg cuts out the middleman. He doesn’t always get snappy, short-attention-span-friendly answers from his guests, but the depth of knowledge behind the answers is immense. The cosmic ray show from a couple of months ago, for example, had a guest who ran cosmic ray detection labs for over thirty years. He happened to be an awfully good explainer, too.
Television, and cable news shows in particular, is where expertise is the most shamefully debased. Yes, the internet is loaded with charlatans and bloviators, but you can find real knowledge if you want to. Cable news shows feature bullshit exclusively, because they rely a continuous stream of talk at all times under all conditions. This is antithetical to expertise, which requires information and reflection. Real experts say “I don’t know” all the time, television experts can’t.
I am acutely aware of my own precarious position. I post scripts here,3 and people trust me to know what I’m doing. But although I’ve been programming since the late 70s (Jesus!), my formal training in computer science is limited to two courses many years ago. That’s one of the reasons I post my full source code and try to explain my scripting choices—so you can judge for yourself and tell me where I’ve gone astray.
And if you see me writing posts about electricity, be especially wary.
Gustav Kirchhoff is probably best known for his electrical work, but structural engineers and stress analysts like me know him for his theory of plate bending and the Piola-Kirchhoff stress tensors. In the preface to their elasticity book, Marsden and Hughes make a joke that’s stuck with me for thirty years:
There are three things that every beginner in elasticity theory should know. The first is that “Kirchhoff” has two h’s in it.
There aren’t many jokes in continuum mechanics, so you take what you can get. Funny or not, it’s kept me from misspelling Kirchhoff since I read it. ↩︎
The EIT, or Engineer in Training, exam was the first of two daylong tests that one needed to take to get a professional engineering license. Its name was later changed to FE, or Fundamentals of Engineering, test, which has a less disrespectful name. Unlike the PE exam (the second test), which one could take only after a certain number of years in professional practice, the EIT could be taken the semester before graduation, and it was commonly given on-campus. The EIT presented several problems across all disciplines of engineering, and you were to solve some subset of them. One of the tricks to taking the EIT was to look for the super-easy problems outside your discipline and save yourself a lot of time. ↩︎
Not so much recently, as work and family obligations have been especially strong. I hope to get back to it soon. ↩︎