Ma Be asked in USMA 19076: >I always thought that the real origin of watt came from the electrical >guys. Perhaps definitionally speaking it may be like Bill described >below. However, I'm talking about *first occurrence*, where did it really >come from and when/how was it first defined/used? Not that it would >matter... ;-)
According to the Encylopaedia Britannica, eleventh edition, the watt was defined by a committee of the British Association. It was reommended by an international Electrical Congress in Chicago in 1893, and finally adopted by the Electrical Congress of 1908 in London. Note that the watt is defined in purely mechanical terms. The power of automobiles in Australia is stated in kilowatts. >So, in essence, as far as I know, the current pool of unit names we have >have pretty much emerged haphazardly without much... "thought" being put >into the process. Therefore, I repeat again, perhaps it should be about >time we address this interesting aspect in SI. Any comments, please? The process was haphazard, but with much serious thought. The latest important arrivals were the pascal and the siemens which were approved by the CGPM in 1971. >On Mon, 25 Mar 2002 23:10:52 > Barbara and/or Bill Hooper wrote: >... The joule per second is a >>derived unit that has a special name: the watt. >... the joule is normally >>defined first as a newton-metre, with the watt being defined later as a >>joule per second... >>The watt is also equal to a volt-ampere... Since the >>volt (V) is a joule per coulomb (J/C) and the coulomb (C) is defined as an >>ampere-second (A7s), it is easy to show that the volt-ampere equals the >>watt: >>1 V7A = (1 J/C)7(1 A) = (1 J/A7s)7(1 A) = 1 J/s = 1 W >... >(There was just a small booboo above. It was supposed to have been J/s, >not J times s as in the original post) > >Marcus The ampere is an SI base unit. The watt is an SI derived unit defined in terms of metre, kilogram and second. The volt is another SI derived unit defined as watt / ampere. The etymology is that definition of the volt depends on the definition of the watt, rather than the other way around. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
