"Jesse Mazer" wrote in message
...


FrediFizzx wrote:

"Jesse Mazer" wrote in message
...
|
|
| Franz Heymann wrote:
|
| "Jesse Mazer" wrote in message
| ...
|
|
| Franz Heymann wrote:
|
|
|
| "Jesse Mazer" wrote in message
| ...
|
|
|
|
| I wrote:
|
|
|
|
|
| Well, you're thinking about it wrong. It would be possible
to
|
|
|
|
| choose
|
|
|
|
| units of mass such that the gravitational constant G was
equal to
|
|
|
|
| 1,
|
|
|
|
| but that wouldn't make it any less real as a physical
| constant--similarly, in cgs units, the basic units of charge
|
|
| (emu)
|
|
|
|
| Sorry, that should be esu...emu is the unit of magnetic
charge in
|
|
|
|
| cgs units.
|
| You might know what you were trying to say both in the
original
| statement and the correction.
| I doubt if anybody else would.
| Comment on this garbage, for instance
| "emu is the unit of magnetic charge in cgs units"
|
|
|
| OK, magnetic moment, I confused my terms, Jeez. I think you
know
|
|
| what I
|
|
| meant.
|
|
|
| No. I had not the foggiest notion. I still do not know what
you are
| trying to say.
| How about being effective by giving a complete sentence with the

| phrase "magnetic moment" in its apropriate place.
| If I were to just replace "magnetic charge" by "magnetic
moment",
the
| sentence would still be garbage, so I feel sure you must be
meaning
| something else.
|
| Franz
|
|
|
|
| You think the sentence "emu is the unit of magnetic moment in cgs
units"
| is garbage? Have a look at this page:
|
| http://www.unc.edu/~rowlett/units/cgsmks.html
|
| It says that emu is the unit of the magnetic dipole moment in CGS
units,
| and that the conversion from CGS to SI is 1 emu = 0.001
Ampere*meter^2.

It is wrong. An emu is a unit of current. It is equal to 10
ampere SI.

FrediFizzx



Well, it's possible you're right since I don't claim to be an expert
in
unit systems, but do you have a source for that? The website above
comes
from a professor of mathematics at the University of North Carolina
at
Chapel Hill, so it seems pretty credible.

I am (was) an expert in the field, having taught E&M for more than a
decade and having performed electrical and magnetic calculations for
sixty years.
Freddi is as wrong as you were. The emu is the name for a complete
set of units for all electrical and magnetic quantities. Quite
analogous to saying that the SI is a complete set of units.

Franz

"Franz Heymann" wrote in message
...
|
| "FrediFizzx" wrote in message
| ...
| "Jesse Mazer" wrote in message
| ...
| |
| |
| | Franz Heymann wrote:
| |
| | "Jesse Mazer" wrote in message
| | ...
| |
| |
| | Franz Heymann wrote:
| |
| |
| |
| | "Jesse Mazer" wrote in message
| | ...
| |
| |
| |
| |
| | I wrote:
| |
| |
| |
| |
| |
| | Well, you're thinking about it wrong. It would be possible to
| |
| |
| |
| |
| | choose
| |
| |
| |
| |
| | units of mass such that the gravitational constant G was
| equal to
| |
| |
| |
| |
| | 1,
| |
| |
| |
| |
| | but that wouldn't make it any less real as a physical
| | constant--similarly, in cgs units, the basic units of charge
| |
| |
| | (emu)
| |
| |
| |
| |
| | Sorry, that should be esu...emu is the unit of magnetic charge
| in
| |
| |
| |
| |
| | cgs units.
| |
| | You might know what you were trying to say both in the original
| | statement and the correction.
| | I doubt if anybody else would.
| | Comment on this garbage, for instance
| | "emu is the unit of magnetic charge in cgs units"
| |
| |
| |
| | OK, magnetic moment, I confused my terms, Jeez. I think you know
| |
| |
| | what I
| |
| |
| | meant.
| |
| |
| |
| | No. I had not the foggiest notion. I still do not know what you
| are
| | trying to say.
| | How about being effective by giving a complete sentence with the
| | phrase "magnetic moment" in its apropriate place.
| | If I were to just replace "magnetic charge" by "magnetic moment",
| the
| | sentence would still be garbage, so I feel sure you must be
| meaning
| | something else.
| |
| | Franz
| |
| |
| |
| |
| | You think the sentence "emu is the unit of magnetic moment in cgs
| units"
| | is garbage? Have a look at this page:
| |
| | http://www.unc.edu/~rowlett/units/cgsmks.html
| |
| | It says that emu is the unit of the magnetic dipole moment in CGS
| units,
| | and that the conversion from CGS to SI is 1 emu = 0.001
| Ampere*meter^2.
|
| It is wrong. An emu is a unit of current. It is equal to 10 ampere
| SI.
|
| Balls. The emu is a complete system of electrical a=nd magnetic units.
| The emu of current is sometimes called the Abamp. (An abbreviation
| for "absolute Ampere")
| 1 Abamp = 10 Amperes

Ok, sounds good to me. I am sure you have had more experience with it
than me. It just that the writer of the following web pages used e.m.u.
in a context that sounded like an emu was also used as the name for the
emu unit of current.

"...1 e.m.u. of current experiences a force of two dynes..."

http://www.ee.surrey.ac.uk/Workshop/...s/unit_systems

FrediFizzx

Franz Heymann wrote:

"Jesse Mazer" wrote in message
...


Franz Heymann wrote:



"Jesse Mazer" wrote in message
...




Franz Heymann wrote:





"Jesse Mazer" wrote in message
...






I wrote:







Well, you're thinking about it wrong. It would be possible to






choose






units of mass such that the gravitational constant G was equal


to






1,






but that wouldn't make it any less real as a physical
constant--similarly, in cgs units, the basic units of charge




(emu)






Sorry, that should be esu...emu is the unit of magnetic charge


in






cgs units.

You might know what you were trying to say both in the original
statement and the correction.
I doubt if anybody else would.
Comment on this garbage, for instance
"emu is the unit of magnetic charge in cgs units"





OK, magnetic moment, I confused my terms, Jeez. I think you know




what I




meant.




No. I had not the foggiest notion. I still do not know what you


are


trying to say.
How about being effective by giving a complete sentence with the
phrase "magnetic moment" in its apropriate place.
If I were to just replace "magnetic charge" by "magnetic moment",


the


sentence would still be garbage, so I feel sure you must be meaning
something else.

Franz






You think the sentence "emu is the unit of magnetic moment in cgs


units"


is garbage?



Yes, assuredly.
The emu, is a generic term which is the name for a complete set of
units encompassing all magnetic and all electrostatic quantities.
What emu is *not* is what you refer to as "the unit of magnetic moment
in cgs units. Moreover there are two differently sized units for
magnetic moment in cgs, namely the cgs emu of magnetic moment and the
cgs esu of magnetic moment.

Have a look at this page:


http://www.unc.edu/~rowlett/units/cgsmks.html

It says that emu is the unit of the magnetic dipole moment in CGS


units,


and that the conversion from CGS to SI is 1 emu = 0.001


Ampere*meter^2.

I don't need to.
What it should say is that 1 emu *of magnetic moment* is the unit of
magnetic dipole moment.
And yes, the conversion factor is correct.

Franz





Well, I was just going by what I read on various webpages describing
units, as I said I'm not an expert on different unit systems. I checked
my E&M textbook, and they don't list any special unit for magnetic
moment, so what you say seems plausible--does that mean the units for
magnetic moment in the e.m.u. system would be abampere*second*cm, and in
the e.s.u. system it'd be statampere*second*cm?

Jesse

Jesse Mazer wrote:



Franz Heymann wrote:

"Jesse Mazer" wrote in message
...


Franz Heymann wrote:



"Jesse Mazer" wrote in message
...




Franz Heymann wrote:





"Jesse Mazer" wrote in message
...






I wrote:







Well, you're thinking about it wrong. It would be possible to






choose






units of mass such that the gravitational constant G was equal


to






1,






but that wouldn't make it any less real as a physical
constant--similarly, in cgs units, the basic units of charge




(emu)






Sorry, that should be esu...emu is the unit of magnetic charge


in






cgs units.

You might know what you were trying to say both in the original
statement and the correction.
I doubt if anybody else would.
Comment on this garbage, for instance
"emu is the unit of magnetic charge in cgs units"





OK, magnetic moment, I confused my terms, Jeez. I think you know




what I




meant.




No. I had not the foggiest notion. I still do not know what you


are


trying to say.
How about being effective by giving a complete sentence with the
phrase "magnetic moment" in its apropriate place.
If I were to just replace "magnetic charge" by "magnetic moment",


the


sentence would still be garbage, so I feel sure you must be meaning
something else.

Franz






You think the sentence "emu is the unit of magnetic moment in cgs


units"


is garbage?



Yes, assuredly.
The emu, is a generic term which is the name for a complete set of
units encompassing all magnetic and all electrostatic quantities.
What emu is *not* is what you refer to as "the unit of magnetic moment
in cgs units. Moreover there are two differently sized units for
magnetic moment in cgs, namely the cgs emu of magnetic moment and the
cgs esu of magnetic moment.

Have a look at this page:


http://www.unc.edu/~rowlett/units/cgsmks.html

It says that emu is the unit of the magnetic dipole moment in CGS


units,


and that the conversion from CGS to SI is 1 emu = 0.001


Ampere*meter^2.

I don't need to.
What it should say is that 1 emu *of magnetic moment* is the unit of
magnetic dipole moment.
And yes, the conversion factor is correct.

Franz





Well, I was just going by what I read on various webpages describing
units, as I said I'm not an expert on different unit systems. I
checked my E&M textbook, and they don't list any special unit for
magnetic moment, so what you say seems plausible--does that mean the
units for magnetic moment in the e.m.u. system would be
abampere*second*cm, and in the e.s.u. system it'd be statampere*second*cm?

Jesse

By the way, is it also true that if you want to refer to electrical
charge in the cgs system, you should say "1 esu of charge" rather than
just "1 esu"? In my textbook "Introduction to Electrodynamics" by David
Griffiths, on p. 518 there is a table of conversion factors where it is
said that the coulomb in the SI system should be converted to the unit
"esu (statcoulomb)" in the cgs system. Is "statcoulomb" really the unit
of charge in the esu. subsystem of cgs units, and "1 esu of charge" is
just a common shorthand for "1 statcoulomb"?

Jesse

"FrediFizzx" wrote in message
...
| "Franz Heymann" wrote in message
| ...
| |
| | "Jesse Mazer" wrote in message
| | ...
| [snip]
| | even though the
| | experiments to determine epsilon_0 and mu_0 have nothing to do with
| | light.
| |
| | No experiments have ever been done to determine the values of eps0 and
| | mu0.
|
| I think what he really meant was k_e in Coulomb's law and k_m in Ampere's
| law (the electric and magnetic constants).
|
| | They are artefacts necessary to define a certain set of units.
| | Such experiments are logically impossible, for the following reasons:
| |
| | mu0 is *defined* to be precisely 4* pi*10^-7
| | and eps0 is *defined* to make eps0*mu0 = c^-2
| | (and c, in turn, has a *defined* value, but we'll let that pass)
|
| The real SI magnetic constant of 2*10^-7 N/A^2 is simply the result of the
| definition of the ampere as a base unit. It was multiplied by an ad hoc
| constant of 2pi. That means that eps0 has an ad hoc value of 1/2pi in it.
| Eps0 = 1/4pi in gaussian cgs units. Take out the ad hoc constant then
| eps0*2pi = 1/2 in gaussian cgs. Which is consistent with what the
following
| link has to say if the magnetic constant is 1/c^2. k_e/k_m = c^2/2
|
| http://www.ee.surrey.ac.uk/Workshop/.../unit_systems/
|
| So what happened to this 1/2 for k_e in gaussian cgs units since k_m is
set
| to 1/c^2? This would mean that in natural units of hbar = c = 1, k_e
should
| be 1/2 and k_m should be 1. k_e = 1/2 got shoved into the product of q*Q
in
| Coulomb's law is what happened in gaussian cgs because they set it to 1.
So
| it seems that the gaussian cgs system is somewhat "*******ized". But the
| big question here then is what the HECK does this 1/2 represent? Well, I
| already told you what I think it represents.

Ok, I think I got this straightened out now. No problem. k_e =
1/(4pi*eps0) is the real SI electric constant. Eps0 has an ad hoc factor of
1/4pi in it. Not 1/2pi. Since k_e = 1 in gaussian units, then k_m = 2/c^2
which is easy to see at the following link,

http://scienceworld.wolfram.com/phys...llelWires.html

And the real SI magnetic constant is mu0/2pi. So the real equation goes
like this,

c^2/2 = (1/4pi*eps0)(2pi/mu0)

So there is no 1/2 factor. Which is good because that was totally messing
me up. The real ratio of the physical length of E_0 to wavelength is 1/2pi.
Not 1/2.

FrediFizzx