Henries

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Henries

Post by Phil White » Mon Oct 08, 2007 11:14 am

I am reliably informed that

1 mean international Henry, = 1.00049~ absolute Henry

Does this also apply in New Zealand? Or is a New Zealand Henry an absolute something else?
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Henries

Post by LoisMartin » Tue Oct 09, 2007 12:50 am

Wow! The things you learn (or almost learn) on WW. I never knew there was a "henry," so I looked it up. It apparently has something to do with physics, which is the one subject I did poorly in in high school. Here's what Merriam-Webster says, and I confess I didn't have enough interest to look up more stuff and figure out what the heck it really is.

the practical meter-kilogram-second unit of inductance equal to the self-inductance of a circuit or the mutual inductance of two circuits in which the variation of one ampere per second results in an induced electromotive force of one volt
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Henries

Post by Shelley » Tue Oct 09, 2007 2:45 am

. . . easy for you to say!
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Henries

Post by Erik_Kowal » Tue Oct 09, 2007 4:13 am

It's very strange that Merriam-Webster decides to call it a "meter-kilogram-second unit" when a less awkward-sounding, more conventional, and more accurate term to use would have been "SI unit" (with "SI" being a reference to the French term "système international d'unités" [EN = "international system of units"] -- in other words, the metric system). It's also not obvious what describing this unit as 'practical' adds to one's understanding of the concept of either the MKS unit or of the henry.

Actually, Wikipedia explains 'henry' far more clearly than M-W does:

"If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry."
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Henries

Post by paulwiggins » Tue Oct 09, 2007 6:13 am

It's an SI measurement ........The unit of inductance, equivalent to the inductance of a closed circuit in which an electromotive force of one volt is produced by a current in the circuit which varies uniformly at the rate of one ampere per second. H [named after Joseph Henry]1 ..... and indeed one my father, a New Zealand radio technician would have been most afmiliar with.


Inductance means that property of a circuit by virtue of which electromagnetic induction takes place. L mutual inductance self-inductance 2. a piece of equipment providing inductance in a circuit or other system; inductor.


The Macquarie adopts the circuit route of definitions
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Post by Tony Farg » Tue Oct 09, 2007 7:46 am

Presumably Merriam Webster is an American beast, and so it is surely no surprise that like in so many other areas it ignores International Systems/agreements/treaties/...
edit: especially one named by cheese eating surrender monkeys
second edit: is there anyone French on this forum? If so please be aware that I don't subscribe at all to that remark.
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Post by Erik_Kowal » Tue Oct 09, 2007 7:55 am

Nice save, Tony. ;-)
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Henries

Post by Bobinwales » Tue Oct 09, 2007 8:16 am

And I thought a Henry was a chinless toff who talked through his nose whilst looking at you down it.

Or does that Henry have to have "Hooray" before it?
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Post by Berale » Tue Oct 09, 2007 2:28 pm

Thanks, Bob, for bringing this discussion down to a level I can understand.
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Henries

Post by Bobinwales » Tue Oct 09, 2007 2:54 pm

My pleasure Meirav, I didn't know what in blue blazes they were talking about either.
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Post by gdwdwrkr » Tue Oct 09, 2007 3:57 pm

I thought it must have been about vodka.
I did enjoy the intro to cheese-eating surrender-monkeys.
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Post by Phil White » Tue Oct 09, 2007 6:01 pm


Originally posted by BobinwalesMy pleasure Meirav, I didn't know what in blue blazes they were talking about either.
I was interested in the precise value of a New Zealand Henry.
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Post by Ken Greenwald » Wed Oct 10, 2007 12:52 am

Phil et al, I too didn’t know the international henry, much less the New Zealand henry (although I did know the familiar henry 1.0), from a hole in the wall, but I found this at Answers.com:
<“Because the explicit laboratory specifications established for the ampere, ohm, and volt were subsequently found to be slightly discrepant from the intent, so was the henry, as a unit derived from them. The IEC of 1908 covered the discrepancy by adopting the distinct name international henry. Because of experimental vagaries, the value for conversions is normally referred to as the mean international henry, = 1.00049 H. There is also the US international henry, = 1.000495 H.”> [[As the units for speed are in km/hr, the units for the henry are volt-seconds/ampere]]
The two common sets of units used in physics are:

1) S.I., usually referred to by physicists as mks/MKS units (meter, kilogram, second)

2) Gaussian, usually referred to by physicists as cgs/CGS units (centimeter, gram, second).

The only time I have ever said (or heard) S.I. or Gaussian as the name of the set of units was in the first week of an introductory physics course when explaining the different systems, but after that it was mks/MKS and cgs/CGS
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Also, it is not unusual in physics for units to be named after scientists who made a major contributions in a particular area.

In the MKS system we have the following units derived from the names of scientists:

Absolute temperature: kelvin (in centigrade degrees) – after William Kelvin

Capacitance: farad (coulombs/volt) – after Michael Faraday

Charge: coulomb (ampere-sec) – after Charles Augustin de Coulomb

Current: ampere (coulomb/sec– after André-Marie Ampere

Electrical potential: volt (joules/coulomb) – after Alessandro Volta

Electrical resistance: ohms (volts/ampere) – after Georg Ohm

Energy and Work: joules (newton-meter or kg-m^2/s^2) – after James Joule

Force: newtons (kilogram-meter/sec^2) – after Isaac Newton

Inductance: henry (volt-sec/ampere) – after Joseph Henry

Magnetic field: tesla (weber/meter^2 or newton/ampere-meter)– after Nikola Tesla [[1 tesla = 10^4 gauss, where the gauss – after Karl Friedrich Gauss is the cgs unit of magnetic field]]

Magnetic flux: weber – after Wilhelm Eduard Weber

Power: watts (joules/sec or kilogram-meter^2/sec^3) – after James Watt

Pressure: pascal (newtons/meter^2 – after Blaise Pascal
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Ken - October 9, 2007
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Henries

Post by LoisMartin » Wed Oct 10, 2007 1:24 am

And you guys are just determined to make me do remedial physics by looking up things like "inductance" and "coulombs." Well, I'll show you and just stay ignorant!
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Post by Ken Greenwald » Wed Oct 10, 2007 1:59 am

Lois, And as they say “ignorance is bliss.” And, incidentally, the unit the bliss in joy/sec was named after the unproductive 20th-century physicist Ignatius Bliss who didn’t discover anything, at least in the area of physics, but who had a legendary girlfriend named Joy.
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