By Mark Frauenfelder at 12:11 pm Wed, Dec 30, 2009
Here's MAKE's Collin Cunningham explaining Ohm's Law: Voltage = Current X Resistance.
What about Cole’s Law?
(thinly sliced cabbage)
When’d it stop being E=IR?
Eh? I’ve never seen it written as E=IR, and I’m a triple-e.
Well, I learned this stuff in the early 1970s…
Ohms Law: E=IR
Watts Law: P=IE
Around the same time I was taught the resistor color code mnemonically as “Black Boys Rape Our Young Girls But Violet Gives Willingly” which was quite memorable, although not in a particularly good way.
–IttÅsai, posting from a machine that cannot login
With a curly E, right? The change to V is because they usually call it “voltage” now, instead of “electromotive force” which isn’t quite as accurate. You must have some fairly old textbooks, because I haven’t seen it for a while.
I prefer the generalized ohm’s law:
j_i = – sigma_ij Delta Phi_j
Phi = Potential
j_i = current density
sigma_ij = conductivity tensor
I like his triangle a lot better than the circle method.
Many years ago, I took-over teaching a 9th grade physical science class. When we got to the unit on electricity, I asked the kids if they had heard of Ohm’s Law.
One kid said, “Yes. Ohm’s Three Laws.”
“Yeah: V = IR , I = V/R , and R = V/I ”
Great timing. I just needed to measure Ohms on my motorcycle’s points ignition last week. I had no idea what I was measuring besides the numbers I was seeing on my multi-meter. Thank you!
E=IR was current up until recent times. The only time I saw V used was in a booklet sold by Radio Shack.
The original degree for electronics was a B.S. in electrical engineering – Electronics major. You ended up knowing a lot more about high voltage transmission lines and motor windings than you did about transistors. That was pulled from the electronics curriculum decades ago.
Back when there were parts houses, one in San Francisco was owned by a man who was an amateur printer. He made some very official looking signs that said “Danger 10,000 Ohms!”
I still remember using Ohm’s Law in Mr. Coutant’s Telecommunications classes at Pasadena City College: “E P E P, I R I R P R I E (pronounced Eep Eep, Ihr Ihr, Pry); Square the Second E, Square the Second I” or E over I R, P over IÂ² R, EÂ² over P R, and P over I E.
I learned in Navy Electronics “A” School ” Twinkle, Twinkle, Little star E = I x R “
We were taught in high school science that this is a common fallacy: E = IR is NOT Ohm’s Law!
E = IR is the definition of resistance.
Ohm’s law states that resistance (thus defined) is nearly constant for a wide variety of metals, and hence it is a useful quantity to quote for a circuit element in the absence of other information about the circuit.
That’s an interesting way to put it. When I see E=IR, it seems pretty clear that R is supposed to be a constant of the material, so it’s stating E and I are directly proportional. That might not be the best way to regard it, but is it really a fallacy?
I find the pace oddly soothing myself. It’s like a lava lamp that teaches you things. Seriously though, I always like his videos. He does a good job of explaining and analogizing electrical concepts in a way that inexperienced people can understand.
Sure he could have just said ‘ohms law is voltage equals current times resistance’ but to someone who doesn’t know what those three things are it’s a pretty meaningless equation.
Ahh, do you really know, since you’re an admittedly inexperienced person, that he really did explain it correctly? Or that his analogies were valid?
(For the anonymous commentators, um, wasn’t this covered in high school?) (What’s called ‘O’ levels in the UK?)
Thanks Collin, a nice little refresher
Doesn’t V deal with straight forward voltage while E or e somehow deals with reactive elements. …Something to do with changing curent in inductors and capacitors, polar coodinates and imaginary numbers? Surely someone knows how to explain this in english (rather than math).
I didn’t like it, sorry. I found it lazy. For spending 7 minutes on this he really should have done a better job of explaining what voltage, current, and resistance really mean. Why is this on MAKE or BoingBoing? I would expect pretty much every geek on these websites to already know Ohm’s law. The people who don’t, whether adults or high-school students, have the most problems visualising what the basic concepts are.
The premise of the video was that this is a major stumbling point in “engineering”. I doubt that, too.
> I would expect pretty much every geek on these websites to already know Ohm’s law.
Some of us are geeks-in-training and want to learn this stuff.
Does he dress like a Blues Brother in all his videos?
I found it very difficult to concentrate on the concept he was trying to explain because of his continuity error. Using a blue pen in one shot, and a grey pen in the other. Very distracting.
“Around the same time I was taught the resistor color code mnemonically as “Black Boys Rape Our Young Girls But Violet Gives Willingly” which was quite memorable, although not in a particularly good way.”
…The Intro to EE class I took at Texas U in 1980 – taught by the mumbling, incoherent Dr. Dougall – was the first time I’d heard “Black” for the first “B”. Dougall had mumbled the mnemomnic, and one of the Black students sitting right behind me asked him to repeat it as he couldn’t believe he’d actually said that with Blacks in the same room. He immediately changed it to “Bad”, which is what High School electronics teachers had been using for years as a mnemonic. The offended student shook his head and said he was going to file a complaint with the EE Dean. We never saw the guy again, and figured he’d gotten pissed and dropped the class…or, knowing what a total choad the Dean was, *he* probably got dropped.
Supposedly it’s better with “black boys” since it lets you remember the black/brown/blue sequence easier.
Personally, I’d like to learn a version that more easily keeps the repeating letters differentiated, something that gives you the Bla – Br – R – O – Y – Gree – Blu – V – Grey – W without having to think about it. I haven’t managed to come up with anything.
The version from bpratt’s chum is certainly memorable, at least! ^_^
I don’t remember what we were officially taught, but I do remember what a fellow student came up with: “Batman Blows Robin On Yonder Gotham Bridge, Very Gooey Work”.
This is what most Ham Radio classes use as well. It is easy to explain and what we describe is to put your finger over the symbol you are looking for and work the math on the chart. Even 9 year olds have mastered this equation. How simple algebra is!
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