Open ericmazur opened 9 years ago
ericmazur
commented
9 years ago Hmmmm... I guess I just get goose bumps when a unit is substituted for a quantity. I check my height with a ruler, not my "meterage". When you stand on a scale, you don't measure your "poundage". But you are right. Is it worth fighting a century of (bad) habits?
JohnDenker
commented
9 years ago A voltage is a quantity, not a unit. The corresponding unit is the volt. Not the same.
Note that gas mileage is /never/ measured in miles. In the US it is measured in miles per gallon, and in Canada it is measured in km per liter ... yet it is still called mileage. On an integrated circuit, acreage is not measured in acres; it is measured in square microns or square nanometers.
The formation of new words by adding "-age" is part of English grammar, and has been for eons. The new word is not equivalent to the root word.
Let's be clear: It would be bad physics and bad grammar to "measure the volts". In contrast, it is conventional and entirely reasonable to measure the voltage. Voltage is in every way better than EMF, and also better than blithering about "potential difference" in cases where the voltage is not a potential.
Breaking the habit is easy. Use a text editor to replace every occurrence of "potential difference" with voltage. In real life, in the physics lab and elsewhere, the habit is already nonexistent; nobody really says "potential difference".
From @JohnDenker: The term "potential difference" is used in chapter 32 in ways that are often misleading and sometimes outright wrong.
Let's cut to the chase: Constructive suggestion: replace every occurrence of "potential" with /voltage/.
RATIONALE: A particularly clear example occurs on page 859 where it says "Often, when analyzing AC circuits, the only things we are interested in are the currents and potential differences."
That would be much, much better if it said "... currents and voltages." The reason is that not every voltage is a potential. Not every electric field is the gradient of a potential. This should be obvious from glancing at the Maxwell equations.
As I like to say at every opportunity: Ideas are primary and fundamental;
terminology is important only insofar as it helps us formulate and communicate the ideas.
In this case we have a clear example of bad terminology. It's bad because it corrupts the ideas. Students who think in terms of voltage can at least have an intelligent discussion of non-potential voltages. In contrast, students who think only in terms of "potential differences" cannot imagine and cannot discuss situations where the thing of interest is not a potential.
Everybody in the real world speaks and thinks in terms of voltage, as they should. This includes electronic engineers, blue-collar electricians, butchers, bakers, and candle-stick makers. The emphasis on "potential difference" seems to be confined to research-based textbooks, and it's another of those things that give "research" a bad name. It's just wrong physics. There are lots of non-potential voltages in this world. -- Generators -- Transformers -- Betatrons -- Ground loops -- et cetera.
It costs nothing to say /voltage/. It's simpler and in every way better.
Back in chapter 31, almost all of the voltages were actually potentials, so I didn't make a fuss about it in that context. However, since voltage is the right concept and the right terminology in general, chapter 31 should be changed in the interests of consistency. Replace every occurrence of "potential" with /voltage/. It can't hurt and it might help.
Voltage is defined as energy per unit charge. Sometimes it's a potential, and sometimes it's not. https://www.av8n.com/physics/voltage-intro.htm