We are all, or should be, extremely familiar with this graphic.

enter image description here

It is course the magic triangle used to represent Ohm's Law.

We should all also be very familiar with the similar power triangle.

enter image description here

What I find curious is that we all instantly recognize and talk about Ohm's law, yet I wonder exactly how many of us know who is responsible for the power triangle.

Even nice tutorial pages like this one, glibly talks about Ohm's Law and then wander into the power triangle as if it is somehow a part of it. No mention is ever given to the actual originators.

In actuality the P=IV law is from Joule heating, Joule's first law, also known as the Joule–Lenz law, discovered independently by James Prescott Joule and Emil Lenz @1842.

Why does Georg Ohm get so much credit while Joule and Lenz, with a law that is, in my mind, equally as important as Ohm's Law, are relegated to the back pages of history?

One has to wonder who slept with whom to either get recognized or forgotten.

I do realize that this seems like a discussion question, but I really want to know if there is some reason not to call it what it is. I do understand that Joule's First Law is a much bigger body of work than just the electrical heating part. Perhaps that is the issue.

Without some reason to the contrary, I'm going to make it my mission to use the credited name for the formula in the future, as, perhaps, should we all.

PS: Interestingly there is no tag on here for the law either. Lenz is not even there and the only mention Joule gets is "Joule-Thief".... sigh

PPS: Ohm's law was published in 1827, I wonder how they figured out how big resistors needed to be for the intervening 15 years...

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    \$\begingroup\$ fun fact: I think I never saw either triangle during my education. Ohm's law ("das ohmsche Gesetz") is a term taught in school – because it's simple enough, I guess. From that fact stems Ohm's "popularity". Lenz's Law ("Lenzsche Regel"), on the other hand, deals with induction – and hence is a far more advanced concept, because it combines multiple "invisible" things that children might have to conceptualize at once; while the "right hand law" of induction, Lorentz force etc is also told in advanced physics classes from grade 9 to 13 in school, Lenz doesn't have the luck of being featured… \$\endgroup\$ Oct 15, 2017 at 15:57
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    \$\begingroup\$ Only recently became aware of the triangle. Ohm's law is so simple, I just remember the one arrangement (E=IR) and rearrange as needed. It never seemed to need a lot of explanation. I do remember some of the guys in class struggling to memorize which arrangement of Ohm's law to use in which circumstances. You don't memorize. You just take the one law, and solve for which ever variable you don't have. Seems easier to me than memorizing a bunch of rules and three equations - or trying to remember which variable belongs where in your triangle. \$\endgroup\$
    – JRE
    Oct 15, 2017 at 16:13
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    \$\begingroup\$ @JRE yes I didn't see these till later in life either, but they do pop into my head when I hear the name now though. \$\endgroup\$
    – Trevor_G
    Oct 15, 2017 at 16:19
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    \$\begingroup\$ On a side note, I think Celsius didn't invent the Celsius scale either. \$\endgroup\$
    – Wesley Lee
    Oct 15, 2017 at 16:22
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    \$\begingroup\$ Great jumping horned toads. That pie chart is horrid. Trying to memorize that would drive me insane. Jeez. The lengths people will go to to avoid a little algebra. \$\endgroup\$
    – JRE
    Oct 15, 2017 at 16:25

1 Answer 1


We do have "Joule heating" as a term for I squared R heating.

For those who like weird graphics, here is a power circle:

enter image description here

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    \$\begingroup\$ My God! Is that a tie? I usually give new people at work this graphics on a post-it. They tend to appreciate it after a while... \$\endgroup\$
    – Dejvid_no1
    Oct 15, 2017 at 19:44
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    \$\begingroup\$ I want that tie! \$\endgroup\$
    – next-hack
    Oct 15, 2017 at 20:00
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    \$\begingroup\$ Yes, it is a tie. My former employer gave them out at one time I have occasionally worn them at Christmas parties, retirement parties etc. \$\endgroup\$
    – user80875
    Oct 15, 2017 at 20:49

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