vaso@mips.COM (Vaso Bovan) (10/30/89)
In article <851@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes: > >Consider this one: how many hams and other electronikers do you know who pro- >nounce dB dee-bee, and how many of them actually know it means decibel? Then, >how many of them have ever heard of a bel? For the real joker, how many of 'em >know what a bel is? It's a lot easier (IMHO) to explain bels than decibels. >Think again: how often do you see something rated in tens of decibels, rather >than bels? WHY? > The bel is of rather recent vintage, 1923 [ A Dictionary of Scientific Units, 4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in continental Europe, the neper is used instead of the bel." Is this true, European readers ?
koning@koning.dec.com (Paul Koning) (10/31/89)
Tesla is the SI unit, gauss the (officially obsolete) unit from the
CGS system. Why is it still used? Partly because we're in the USA,
where the metric system is only barely understood. Partly because
engineers and amateurs tend not to care much about consistency in
units.
I still remember the grief I caught from my Physics prof. because I
had the nerve to write up a lab report on gamma ray experiments with
the energies listed in fJ (femtojoules) rather than his pet MeV
(megaelectronvolts, a mishmash if ever I saw one).
Does all this matter, you ask? It sure does. I recently tried to
read an apparently well-regarded textbook on switching power supplies.
The section on inductor design was totally unintellegible. The
reason: careless random mixing of units, particularly centimeters
or square centimeters vs. "circular mils" [sic].
paul, ni1d
PS. Remember the Hz vs. cps flaming in QST some years ago?jk3k+@andrew.cmu.edu (Joe Keane) (10/31/89)
But _everyone_ knows 1 Tesla = 10^4 gauss. Fortunately, SI are slowly taking over. Question: How do you usually measure thermal conductivity in British units? Answer: (Btu / hr) / (ft^2) / (*F / in) Put that in your units program and smoke it! I'll take watts / meter-*K.
jgh@root.co.uk (Jeremy G Harris) (10/31/89)
In article <30339@buckaroo.mips.COM> vaso@mips.COM (Vaso Bovan) writes: >The bel is of rather recent vintage, 1923 [ A Dictionary of Scientific Units, >4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in >continental Europe, the neper is used instead of the bel." Obsolete, I think. A faint memory tells me that the neper is natural-log based rather than log-base-10 based. Never seen it used. -- Jeremy Harris jgh@root.co.uk
dillon@jumbo.dec.com (John Dillon) (11/01/89)
In article <5817@shlump.nac.dec.com>, koning@koning.dec.com (Paul Koning) writes: > > Tesla is the SI unit, gauss the (officially obsolete) unit from the > CGS system. Why is it still used? Partly because we're in the USA, > where the metric system is only barely understood. Partly because > engineers and amateurs tend not to care much about consistency in > units. Ahh, unit bigotry! Just what we need. The author suggests that SI units are the answer regardless of the question. It is true that several systems of units carry an enormous burden of historical chaos, but the CGS system is NOT one of them. In fact, were it not for the burden of real-life test instruments calibrated in volts and amps, a person seriously schooled in classical electrodynamics would choose to work in either the CGS or Heaviside-Lorentz systems*. If you wish to explore this further, I would suggest reading J.D. Jackson's "Classical Electrodynamics", which has an excellent appendix on units and dimensions. > I still remember the grief I caught from my Physics prof. because I > had the nerve to write up a lab report on gamma ray experiments with > the energies listed in fJ (femtojoules) rather than his pet MeV > (megaelectronvolts, a mishmash if ever I saw one). This makes as much sense as complaining about astronomers' use of parsecs and light-years. The use of electron-volt (eV) and its derivatives in this assignment gives the student familiarity and appreciation of it's utility. Ignoring the utility misses the point. That utility is the same as the real-world utility of SI units. Sure, many folks have amused themselves by computing plate tectonic movement in mils per fortnight or microchip die area in femto-acres. To be saddled with systems of units where this a constant necessity would be a horror. But even more horrible would be an educational system which did not teach students to cope with the various units found in the real world, or to take advantage of specialized units where practical. -- John * extra credit question: do you know why the vacuum permeability in rationalized MKSA (a subset of SI) is exactly 4*pi*1e-7 ? If not, please direct flames to /dev/null.
torkil@psivax.UUCP (Torkil Hammer) (11/01/89)
In article <30339@buckaroo.mips.COM> vaso@mips.COM (Vaso Bovan) writes:
#The bel is of rather recent vintage, 1923 [ A Dictionary of Scientific Units,
#4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in
#continental Europe, the neper is used instead of the bel." Is this true,
#European readers ?
Nobody I knew of used neper. Isn't it supposed to pertain to RF levels?
Nobody used bels either. But everybody used decibels about sound levels.
And volume was something we measured in cubic meter.
Which leads to the next interesting question: Why is sound level or
sound level control called 'volume?'vaso@mips.COM (Vaso Bovan) (11/01/89)
In article <14184@jumbo.dec.com> dillon@jumbo.dec.com (John Dillon) writes: >In article <5817@shlump.nac.dec.com>, koning@koning.dec.com (Paul Koning) writes: >> >> Tesla is the SI unit, gauss the (officially obsolete) unit from the >> CGS system. Why is it still used? Partly because we're in the USA, >> where the metric system is only barely understood. Partly because >> engineers and amateurs tend not to care much about consistency in >> units. > >Ahh, unit bigotry! Just what we need. The author suggests that >SI units are the answer regardless of the question. > >It is true that several systems of units carry an enormous burden >of historical chaos, but the CGS system is NOT one of them. In fact, >were it not for the burden of real-life test instruments calibrated >in volts and amps, a person seriously schooled in classical >electrodynamics would choose to work in either the CGS or >Heaviside-Lorentz systems*. If you wish to explore this further, >I would suggest reading J.D. Jackson's "Classical Electrodynamics", >which has an excellent appendix on units and dimensions. > >-- John Which CGS system do you prefer: electromagnetic or electrostatic ? Should I have to remember that 1 abvolt = 10^-8 practical volts and 1 abampere = 10 practical amperes ? Or is easier that 1 stat volt = 300 practical volts, and 1 stat ampere = (1/3)10^-9 practical amperes ? Which system do you recommend ? > >* extra credit question: do you know why the vacuum permeability >in rationalized MKSA (a subset of SI) is exactly 4*pi*1e-7 ? For bonus points, explain why the CGS electromagnetic unit of capacitance is the gigafarad.
cees@maestro.htsa.aha.nl (Cees Keyer) (11/01/89)
In article <1038@root44.co.uk> jgh@root44.UUCP (Jeremy G Harris) writes: +>In article <30339@buckaroo.mips.COM> vaso@mips.COM (Vaso Bovan) writes: +>>The bel is of rather recent vintage, 1923 [ A Dictionary of Scientific Units, +>>4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in +>>continental Europe, the neper is used instead of the bel." In Europe we use the bell instead of the neper. The bell is a measure for good things but is a large unit hence picobello :-). +> +>Obsolete, I think. A faint memory tells me that the neper is natural-log based +>rather than log-base-10 based. Never seen it used. +>-- The neper is used in transmision technology. -- DISCLAIMER: I am not insane, I am a plane. pjew! Cees Keyer, Algemene Hogeschool Amsterdam. | fax: (+31) 20-443215 department of electrical engineering. | phone (+31) 20-429333 Email: cees@maestro.htsa.aha.nl cees@tamtam.htsa.aha.nl Snail: AHA-TMF, Europaboulevard 23, 1079 PC Amsterdam, The Netherlands.
jgd@rsiatl.UUCP (John G. De Armond) (11/02/89)
In article <2917@psivax.UUCP> torkil@psivax.UUCP (Torkil Hammer) writes: >Nobody used bels either. But everybody used decibels about sound levels. >And volume was something we measured in cubic meter. >Which leads to the next interesting question: Why is sound level or >sound level control called 'volume?' That's easy. The control varies how many cubic feet of sound get produced by the speakers. Didn't you know that the standard bell (of the church variety) held about 1 cubic foot? Or that the home version was about a tenth as spaceous, ergo the decibel? Of course, if you have a hundred or so of these decibels, the great pressure of the large volume of sound, especially the higher density sounds, can cause damage such as cracked plaster, damaged ear drums and so on. Oh yeah, .... :-) John -- John De Armond, WD4OQC | Manual? ... What manual ?!? Radiation Systems, Inc. Atlanta, GA | This is Unix, My son, You emory!stiatl!rsiatl!jgd **I am the NRA** | just GOTTA Know!!!
henry@utzoo.uucp (Henry Spencer) (11/02/89)
In article <30542@buckaroo.mips.COM> vaso@mips.COM (Vaso Bovan) writes: >For bonus points, explain why the CGS electromagnetic unit of capacitance >is the gigafarad. Now *there's* a filter capacitor! -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
larry@kitty.UUCP (Larry Lippman) (11/04/89)
In article <1989Nov2.024305.10583@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <30542@buckaroo.mips.COM> vaso@mips.COM (Vaso Bovan) writes: > >For bonus points, explain why the CGS electromagnetic unit of capacitance > >is the gigafarad. > > Now *there's* a filter capacitor! Yup, that's a pretty large unit. Actually, I've not heard of the term gigafarad, although the CGS emu unit of the abfarad would be 10^9 farads. I suspect that emu folks who deal in abvolts, abamperes, abohms, and abcoulombs would prefer to stay with abfarads instead of gigafarads, though. Now, for a unit that is truly bizarre, consider the reciprocal of capacitance, referred to as "elastance", which is measured in "darafs". I kid you not. For those Net readers who deal with purchasing departments, for some fun, next time you need a small ceramic disc capcitor, specify the capacitor value in elastance using the unit of gigadaraf. :-) <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"