Standing around in the cold for a few hours yesterday, then driving for almost five hours has given the cold SteelyKid had a week or so ago the opening it needed to infect me, so I’m all hoarse and achy this morning. Which means you get silly blogging, such as this poll inspired by some edits I had to make to this week’s lab in the intro E&M class I’m teaching:
I know you’d like to be able to click more than one answer. Life’s tough. Get a helmet.
A cruel trick played on those of us who are color blind.
…You still use leaded resistors?
…And you still think colds are caused by getting cold?
No, I think colds are caused by viruses. I had the beginning of this one days ago. Spending a bunch of time standing around in the cold tends to aggravate them, though, presumably because energy that ought to be going to fight the infection is instead being expended trying to keep from freezing. That’s what happened here– I was keeping the cold at bay until I was distracted by the stress of the last few days (10-ish hours in the car, a not terribly good night of sleep in a hotel, and several hours of standing around in the cold and damp).
If there’d been an option in the survey for “out-moded and really annoying” I would have chosen that. Like Grad says, it’s not exactly a helpful scheme for the colorblind (the same goes for plots that use different colors for different functions, but don’t also use a different pattern of line), and even for those of us who can see all the colors, trying to tell the difference between red, orange, yellow, brown, AND gold is nearly impossible. Especially when you’re digging the resistors out of the bin in the lab and can’t trust the last class to have put them back in the right place…
Seriously. Just print the damn numerical value and provide a magnifying glass.
One of my recently retired colleagues continued to teach “Bad Boys Ravish…” The rest of us were in disbelief that he thought that was OK.
The real fun comes when you encounter precision resistors which use the color code. Ordinary resistors (tolerance 5% or more) can cope with two significant figures, but you can also buy resistors with 1% tolerance, and they need three significant figures to specify the resistance. Which can be a surprise when you expect that third band to refer to an exponent.
Jaime’s proposed solution has been in use for capacitors for at least a couple of decades: you get a three-digit code consisting of two significant figures and an exponent. The reference value is 1 pF, so for example the code 104 means 10 * 10^4 pF, or 0.1 μF.
Color codes were also used for other components, especially capacitors. ‘Secondary’ characteristics could also be coded. There are lotsa pretty color code charts available through your friendly favorite search engine.
Learnt those at some point as a kid, and I have happily forgotten all about them in the intervening 20-odd years.
I’ll pile on and say that I always use 1% metal film resistors on which the resistance is printed clearly (well, you’ve gotta remember what the stupid ‘R’ means for small resistances). I never found that I could work that – or pretty much any other – mnemonic. I might as well just memorize the color code and be done with it.
“Ravish”? My dad taught it to me the way he learned it in the Navy … and you left off “for gold or silver”.
The alternative “Bad booze rots our young guts but …” isn’t much better. None of these are politically correct because they originate in the electronics industry, not the academy, but I figure the only way to expunge sexism is to expose it and teach the alternative.
And the alternative is that the colors themselves are easy because the visible spectrum (but just ROYGBV, because Indigo ended up on your jeans) makes up the bulk of it. And since Black and White are obvious, you really just need a way to remember where brown and gray are located — and brown and gray are just variants of black and white.
It isn’t complicated. The phrase is just for dimwits.