I just sent a note off to Will Shortz about an error in the NY Times crossword puzzle. Here’s what I said.
Pretty much every time that I think I've noticed an error in the Times crossword, the error turns out to be mine. But as a physicist and physics teacher, I'm confident about this one. In Saturday's puzzle, 59 down is defined as "Energy expressed in volts: Abbr.", and the answer is "EMF". This definition is incorrect. An EMF is generally expressed in volts, but it's not an energy. In fact, the volt isn't even a unit of energy, so "energy expressed in volts" is sort of like "distance expressed in pounds" or "speed expressed in dollars."
EMF is a form of voltage, or equivalently of electric potential (these two are synonyms). Another way to say it is "energy per charge", but that "per charge" part is very important. For instance, a car battery supplies an emf of 12 V, which is less than the emf of a pair of 9-volt batteries. But despite the relatively small emf, the car battery has a lot more energy stored in it than the two 9-volts.
By the way, you probably don't remember me, but we spoke on the phone about 10 years ago: I was an on-air participant in the NPR puzzle. You stumped me with "Pal Joey", but other than that I did OK.
By the way, emf is a good candidate for the most misleading name in physics: the F stands for “force”, but in addition to not being an energy, emf isn’t a force either. At least one textbook (I can’t remember which) says that you shouldn’t think of EMF as standing for anything, putting it in the same category as KFC and the AARP. (The Oakland A’s used to be in this category too, but I think they’re not anymore.)