magnetic field

[Don Kelly]

"Ken" <lera@sympatico.ca> wrote in message
news:yLH5d.2351$MD5.146609@news20.bellglobal.com...

Hi,

I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.

thank you

ken

A field is a region of influence- hence a magnetic field is a region of

magnetic influence- i.e. there are effects due to the magnetism. Beyond that
one gets into "what is magnetism"
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

 

[Kevin Kilzer]

On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:

I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.

Basically, both electric and magnetic fields store electromagnetic
enegy. Electric fields can be created by something as simple as a
battery, and magnetic fields come from magnets or from electrical
coils while a current flows. Why magnets make magnetic fields is a
question for quantum physics.

With respect to Sylvia, James Clerk Maxwell expressed a relationship
between electric and magnetic fields in the mid 1800's. Maxwell's
contribution was to show that a magnetic field is created as an
electric field changes, and an electric field is created as a magnetic
field changes. The result is that if I switch an electric field off
and on, I get a magnetic field that swells and collapses with each
on-off transistion.

If I flip the swith fast enough at some frequency, I will find that
the magnetic field comes and goes with the same frequency. But, since
a changing magnetic field will create its own electric field, the
effect moves out to this new field, which makes another magnetic
field, and so on, and that is radio.

Kevin

 

[Sylvia Else]

Kevin Kilzer wrote:

On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:


I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.


Basically, both electric and magnetic fields store electromagnetic
enegy. Electric fields can be created by something as simple as a
battery, and magnetic fields come from magnets or from electrical
coils while a current flows. Why magnets make magnetic fields is a
question for quantum physics.

With respect to Sylvia, James Clerk Maxwell expressed a relationship
between electric and magnetic fields in the mid 1800's. Maxwell's
contribution was to show that a magnetic field is created as an
electric field changes, and an electric field is created as a magnetic
field changes. The result is that if I switch an electric field off
and on, I get a magnetic field that swells and collapses with each
on-off transistion.

If I flip the swith fast enough at some frequency, I will find that
the magnetic field comes and goes with the same frequency. But, since
a changing magnetic field will create its own electric field, the
effect moves out to this new field, which makes another magnetic
field, and so on, and that is radio.

Kevin

I'm not disagreeing with Kevin, but there is a simple thought experiment
that shows how careful one must be about taking a theory, such as that
of James Clerk Maxwell, and attempting to use it as anything more than a
description.

Take two electrons, separated in space, stationary relative to some
observer. There's an electric field, obviously, but no magnetic field.
Now take another observer moving perpendicularly to the line joining the
electrons. This observe sees the electrons in motion. Electrons in
motion are an electric current, and an electric current produces a
magnetic field, so for that observer there is a magnetic field present.

So one observer finds a magnetic field present where another observer
finds none. The notion that a magnetic field has a concrete existence is
clearly problematic. This paradox doesn't appear in the theory itself,
because it simply tells you what will happen (or more exactly, what your
measurements will show). It doesn't say anything about what is "really"
there.

Sylvia.

 

[TimPerry]

Kevin Kilzer wrote:

On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:


I would like to know what is a magnetic field. I mean what is it
composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.

i was pretty sure that the magnetic field was the horizontal plane where
alnico, samarium cobalt, and neodymium magnets were stored prior to
instillation in speakers and microphones.

but after some consideration i decided it must be a nickname for 3M stadium.


perhaps its just a wild gauss chase but i wouldn't get too fluxed up over
it.

 

[John]

Take two electrons, separated in space, stationary relative to some
observer. There's an electric field, obviously, but no magnetic field.
Now take another observer moving perpendicularly to the line joining the
electrons. This observe sees the electrons in motion. Electrons in
motion are an electric current, and an electric current produces a
magnetic field, so for that observer there is a magnetic field present.

So one observer finds a magnetic field present where another observer
finds none. The notion that a magnetic field has a concrete existence is
clearly problematic. This paradox doesn't appear in the theory itself,
because it simply tells you what will happen (or more exactly, what your
measurements will show). It doesn't say anything about what is "really"
there.

This is all a bit over my head, but presumably the first observer (the one

who doesn't see the magnetic field because it doesn't exist for him) sees
something else; whatever the second observer sees as a magnetic field
manifests itself somehow for the first observer? Don't conservation laws
say that elements might vary, but the total sum must be the same?
Probably not...

 

[Repeating Rifle]

in article drvel0p49rt7vhp64ieosgsarumo7ghsc8@4ax.com, Kevin Kilzer at
kkilzer.remove.this@mindspring.com wrote on 9/26/04 7:59 PM:

Basically, both electric and magnetic fields store electromagnetic
enegy. Electric fields can be created by something as simple as a
battery, and magnetic fields come from magnets or from electrical
coils while a current flows. Why magnets make magnetic fields is a
question for quantum physics.

Whatever a magnetic field may be, quantum physics is not going to explain
it. Quantum physics will merely use the magnetic field as part of the
hamiltonian in a quantum equation such as the Schrödinger equation. From
that, quantum consequences of magnetic field will be derived but not
explained.

Bill

 

[Repeating Rifle]

in article 4157853f$0$20129$afc38c87@news.optusnet.com.au, Sylvia Else at
sylvia@not.at.this.address wrote on 9/26/04 8:13 PM:

Take two electrons, separated in space, stationary relative to some
observer. There's an electric field, obviously, but no magnetic field.
Now take another observer moving perpendicularly to the line joining the
electrons. This observe sees the electrons in motion. Electrons in
motion are an electric current, and an electric current produces a
magnetic field, so for that observer there is a magnetic field present.

So one observer finds a magnetic field present where another observer
finds none. The notion that a magnetic field has a concrete existence is
clearly problematic. This paradox doesn't appear in the theory itself,
because it simply tells you what will happen (or more exactly, what your
measurements will show). It doesn't say anything about what is "really"
there.

Think special theory of relativity and Lorentz transformation. Realize that
both electric field and magnetic field are part of a tensor, that is
relatavisticly invariant.

What is a tensor you my ask. Rather than giving a circular argument I will
present *stress* as an example. Inside a stressed medium there will be a
combination of tensile and shear stresses. This combination is an entity by
itself, in which tensile and shear stresses cannot be separated out. If you
carefully twist a piece of blackboard chalk (if it still is available)
without bending it, it will break with a 45 degree break. Even though you
are applying rotational shear alone, there are directions, at 45 degrees to
the shear where tension is produced. The chalk is weaker in tension than in
shear and the tension ends up causing the break. Stress is a tensor that is
an entity where where shear and tension are not independently present.

The same is true for electric and magnetic fields. The entity is a tensor
that mixes electric and magnetic fields.

Bill

I

 

[Repeating Rifle]

in article RAM5d.5110$5H2.4507@news01.roc.ny, John at John@john.com wrote on
9/26/04 9:23 PM:

This is all a bit over my head, but presumably the first observer (the one
who doesn't see the magnetic field because it doesn't exist for him) sees
something else; whatever the second observer sees as a magnetic field
manifests itself somehow for the first observer? Don't conservation laws
say that elements might vary, but the total sum must be the same?
Probably not...

Whatever one observer sees is what another observer sees when transformed ty
the appropriate Lorentz transformation.

Bill

 

[Checkmate]

On Mon, 27 Sep 2004 13:13:03 +1000, Sylvia Else put forth the notion
that...

Kevin Kilzer wrote:

On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:


I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.


Basically, both electric and magnetic fields store electromagnetic
enegy. Electric fields can be created by something as simple as a
battery, and magnetic fields come from magnets or from electrical
coils while a current flows. Why magnets make magnetic fields is a
question for quantum physics.

With respect to Sylvia, James Clerk Maxwell expressed a relationship
between electric and magnetic fields in the mid 1800's. Maxwell's
contribution was to show that a magnetic field is created as an
electric field changes, and an electric field is created as a magnetic
field changes. The result is that if I switch an electric field off
and on, I get a magnetic field that swells and collapses with each
on-off transistion.

If I flip the swith fast enough at some frequency, I will find that
the magnetic field comes and goes with the same frequency. But, since
a changing magnetic field will create its own electric field, the
effect moves out to this new field, which makes another magnetic
field, and so on, and that is radio.

Kevin


I'm not disagreeing with Kevin, but there is a simple thought experiment
that shows how careful one must be about taking a theory, such as that
of James Clerk Maxwell, and attempting to use it as anything more than a
description.

Take two electrons, separated in space, stationary relative to some
observer. There's an electric field, obviously, but no magnetic field.
Now take another observer moving perpendicularly to the line joining the
electrons. This observe sees the electrons in motion. Electrons in
motion are an electric current, and an electric current produces a
magnetic field, so for that observer there is a magnetic field present.

So one observer finds a magnetic field present where another observer
finds none. The notion that a magnetic field has a concrete existence is
clearly problematic. This paradox doesn't appear in the theory itself,
because it simply tells you what will happen (or more exactly, what your
measurements will show). It doesn't say anything about what is "really"
there.

Sylvia.

I think Heisenberg first developed that theory, but I'm not certain.

--
Checkmate

 

[E. Rosten]

Repeating Rifle wrote:

What is a tensor you my ask. Rather than giving a circular argument I
will
present *stress* as an example. Inside a stressed medium there will be a
combination of tensile and shear stresses. This combination is an
entity by
itself, in which tensile and shear stresses cannot be separated out.

Shear stress can always be seperated out: you can represent any
combination of shear and tensile stress as pure tensile stress (google
for Mohr's Circle).

The Mohr's Circle operation is just a graphical way of diagonalizing the
stress matrix (well, it only works in 2D where the tensor is of rank 2).


-Ed

--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

 

[E. Rosten]

Bob Ward wrote:

The only hope RS (or any other retailer) has, is its customer base.
With condescending assholes in the field, it can only get worse.
I'll tell you: Every time I walk into a RS store, I express my feelings,
and they are not ALL good. For instance: They are carrying less and less in
the way of discreet electronics components, like IC's, connectors, small
accessories, and even resistors and capacitors. I tell them that. But I do
it constructively. Will it get better? Probably not. It's largely driven by
the market trend.



Is there a discreet way to point out the difference between "discrete"
and "discreet"?

I want discreet components. You know, ones that do the job quietly
without making a fuss or goddiping or any of that stuff. Resistors
should be seen and not heard. Incedentelly that is why I prefer
resistors to, say, capacitors. At worst a resiztor makes a small fizzing
sound (but that is rare). My capacitors on the other hand often make
loud bangs. That is about as indiscreet as it gets.

-Ed



--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

 

[CWatters]

"Ken" <lera@sympatico.ca> wrote in message
news:yLH5d.2351$MD5.146609@news20.bellglobal.com...

Hi,

I would like to know what is a magnetic field. I mean what is it composed
of.

It isn't really composed of anything. It's a region in which a magnetic
force can be detected. Ever seen a police car on the motorway? Everyone
within 100 yards drives exactly at the speed limit. the police call this a
bubble or zone of legality. The zone isn't composed of anythig but you can
"feel the force".

 

[Ed Price]

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:46qdl0det9etq6864tgfk3dejg1uuqp6dq@4ax.com...

On Sun, 26 Sep 2004 03:48:08 -0700, "Ed Price" <edprice@cox.net> wrote:

Radio Shack used to be (maybe 30 years ago) an intriguing place to browse
and buy project parts. But for whatever reason, the selection and quality
of
discrete components has plummeted to the joke level. It was bad 10 years
ago, and it's even worse now.

My proof? Well, I can go into any store in the San Diego region, and get
the
same level of cheap parts. From what I hear on Usenet, this is typical
everywhere else. You could refute my experience, if you could cite a Radio
Shack that sells RG-214 coax, type N coax fittings, or switches that have
tin-plated terminals and a good "feel."

I don't have a citation/link (it's been several weeks since I read it)
but a recent industry rag had an article commenting that Radio Shack
might be returning at least partway to its roots. They apparently had a
"D'Oh!" moment and realized that there's no possible way to compete with
the warehouse retailers for the big ticket items. A typical RS has less
total shelf space than in just the notebook PC aisle at CompUSA.

On the other hand, a customer driving to CompUSA (or fill-in-the-blank)
probably passes at least a couple RS stores en route. So they're looking
to capture the "I need a ..." market for smaller items and piece parts.

I wish them luck. It is, perhaps, a sign of uber-geek sophistication to
dump on Radio Shack. But, even in the days of on-line ordering and
overnight delivery, it's pretty handy to be able to walk a couple of
blocks to the local RS and pick up a spool of wire-wrap wire.

--
Rich Webb Norfolk, VA

Not dumping on them, it's more like wondering how an old friend went over to
the dark side. RS just might have some wire-wrap wire. Do you think they
also have wrapping tools, suitable DIP sockets, switches with WW compatible
terminals, and maybe even an IC or two? Analog & logic stuff is not mutually
incompatible with RF, but I just notice the RS lack of RF components more
acutely.

Thus far, based on my last visit of a week ago, there's no evidence of any
new emphasis on component selection or quality. Fortunately for me, I have a
nearby Gateway, and a couple of big surplus stores too. Each has their
strengths, and I try my best to keep them all profitable. NAPA too! <g>

Ed
wb6wsn

 

[softh@bellsouth.net]

On Mon, 27 Sep 2004 03:13:03 UTC, Sylvia Else
<sylvia@not.at.this.address> wrote:

Kevin Kilzer wrote:

On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:


I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.


Basically, both electric and magnetic fields store electromagnetic
enegy. Electric fields can be created by something as simple as a
battery, and magnetic fields come from magnets or from electrical
coils while a current flows. Why magnets make magnetic fields is a
question for quantum physics.

With respect to Sylvia, James Clerk Maxwell expressed a relationship
between electric and magnetic fields in the mid 1800's. Maxwell's
contribution was to show that a magnetic field is created as an
electric field changes, and an electric field is created as a magnetic
field changes. The result is that if I switch an electric field off
and on, I get a magnetic field that swells and collapses with each
on-off transistion.

If I flip the swith fast enough at some frequency, I will find that
the magnetic field comes and goes with the same frequency. But, since
a changing magnetic field will create its own electric field, the
effect moves out to this new field, which makes another magnetic
field, and so on, and that is radio.

Kevin


I'm not disagreeing with Kevin, but there is a simple thought experiment
that shows how careful one must be about taking a theory, such as that
of James Clerk Maxwell, and attempting to use it as anything more than a
description.

Take two electrons, separated in space, stationary relative to some
observer. There's an electric field, obviously, but no magnetic field.
Now take another observer moving perpendicularly to the line joining the
electrons. This observe sees the electrons in motion. Electrons in
motion are an electric current, and an electric current produces a
magnetic field, so for that observer there is a magnetic field present.

So one observer finds a magnetic field present where another observer
finds none. The notion that a magnetic field has a concrete existence is
clearly problematic. This paradox doesn't appear in the theory itself,
because it simply tells you what will happen (or more exactly, what your
measurements will show). It doesn't say anything about what is "really"
there.

Sylvia.

Hi Sylvia,

Just a little note here, in your post the observer is moving relative
to the electrons not the electrons relative to each other so there is
no change in the electric potentials, unless the observer is at a
different electrical potential themselves, of course then they are not
a 'neutral observer" so the stationary observer would then see the
field created as the other non stationary observer moved past the
stationary electrons. The question I come up with is exactly what does
the "at differential" moving observer see, since they are part of the
emf/cemf event.

Matt





--
"It's not what folks don't know that gets 'em in the most trouble,
it's the things they do know that ain't so" Will Rodgers

"Any sufficiently advanced technology appears as magic" Arthur C.
Clarke

 

[Repeating Rifle]

in article cj8eqs$9kd$0@pita.alt.net, Checkmate at LunaticFringe@The.Edge
wrote on 9/27/04 12:15 AM:

I think Heisenberg first developed that theory, but I'm not certain.

Planck introduce the concept of a quantum of energy in order to explain the
spectral distribution of black body radiation. Einstein and others were able
to extend the concept to explain specific heat and photoemission. Bohr first
applied it to atomic physics. Heisenberg developed the first modern theory
of quantum mechanics. Shrödinger formulated a wave equation that was much
more familiar to physicists of the day. The big surprise was that the
Schrödinger formulation gave identical results to that of Heisenberg's in
spite of appearing to be very different. The Schrödinger formulation was
much easier for making calculations while the Heisenberg formulation was
better suited to understanding essence of what quantum physics was all
about.

Bill

 

[Repeating Rifle]

in article 4157DE09.1070909@my.sig, E. Rosten at look@my.sig wrote on
9/27/04 2:31 AM:

Shear stress can always be seperated out: you can represent any
combination of shear and tensile stress as pure tensile stress (google
for Mohr's Circle).

The Mohr's Circle operation is just a graphical way of diagonalizing the
stress matrix (well, it only works in 2D where the tensor is of rank 2).

Mohr's circle is a tensor on the cheap. In a sense, it was developed for
engineers who were not formally trained in tensors or their matrix
representations. The days when that was necessary, I hope, are over.

Another crutch for tensors was developed under the name of *dyadics*.

Another example of tensor quantities is that of the dielectric constant
tensor. Displacement (D field) is not in the direction of the electric field
(E field) for an anisoptripic material like a crystal.

Even more complicated are the piezo-elasto-optic tensors used for
electro-optic devices where there are simultaneous stresses and optical
index changes.

Bill

 

In alt.engineering.electrical John <John@john.com> wrote:
|
|>
|> Take two electrons, separated in space, stationary relative to some
|> observer. There's an electric field, obviously, but no magnetic field.
|> Now take another observer moving perpendicularly to the line joining the
|> electrons. This observe sees the electrons in motion. Electrons in
|> motion are an electric current, and an electric current produces a
|> magnetic field, so for that observer there is a magnetic field present.
|>
|> So one observer finds a magnetic field present where another observer
|> finds none. The notion that a magnetic field has a concrete existence is
|> clearly problematic. This paradox doesn't appear in the theory itself,
|> because it simply tells you what will happen (or more exactly, what your
|> measurements will show). It doesn't say anything about what is "really"
|> there.
|>
| This is all a bit over my head, but presumably the first observer (the one
| who doesn't see the magnetic field because it doesn't exist for him) sees
| something else; whatever the second observer sees as a magnetic field
| manifests itself somehow for the first observer? Don't conservation laws
| say that elements might vary, but the total sum must be the same?
| Probably not...

If there is motion between the observer and the electrons, the observer
might THINK he sees a magnetic field. But is it really there? That lies
in the ability to observe. How do you tell if a magnetic field is there
or not? You measure it by seeing how it acts on something. One way is
with a coil and ampmeter. But now that's electrons again. The net effect
is that something which is electrically changed has ultimately caused an
electrical current where movement is involved.

On the other hand, how do we know there is an electron there? Maybe it
only looks like it because that would explain a magnetic field, which is
what we are measuring. Maybe what we sense as an electric/static charge
is really a sensation of a magnetic current because we have to move in
some way to know there is a charge and where it is.

One cannot be without the other, but the real question is whether there
are really two things or not. I suggest that the answer is that what is
really there is one thing that simply is characterizsed both ways.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

 

In alt.engineering.electrical CWatters <colin.watters@pandorabox.be> wrote:

| It isn't really composed of anything. It's a region in which a magnetic
| force can be detected. Ever seen a police car on the motorway? Everyone
| within 100 yards drives exactly at the speed limit. the police call this a
| bubble or zone of legality. The zone isn't composed of anythig but you can
| "feel the force".

It is composed of something called "fear".

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

 

[No Spam]

Repeating Rifle wrote:

in article cj8eqs$9kd$0@pita.alt.net, Checkmate at LunaticFringe@The.Edge
wrote on 9/27/04 12:15 AM:


I think Heisenberg first developed that theory, but I'm not certain.


Planck introduce the concept of a quantum of energy in order to explain the
spectral distribution of black body radiation. Einstein and others were able
to extend the concept to explain specific heat and photoemission. Bohr first
applied it to atomic physics. Heisenberg developed the first modern theory
of quantum mechanics. Shrödinger formulated a wave equation that was much
more familiar to physicists of the day. The big surprise was that the
Schrödinger formulation gave identical results to that of Heisenberg's in
spite of appearing to be very different. The Schrödinger formulation was
much easier for making calculations while the Heisenberg formulation was
better suited to understanding essence of what quantum physics was all
about.

Bill

And I thought Checkmate was being funny. ;-)

 

[Clint Sharp]

In message <cj9voq11lop@news2.newsguy.com>, phil-news-nospam@ipal.net
writes

In alt.engineering.electrical CWatters <colin.watters@pandorabox.be> wrote:

| It isn't really composed of anything. It's a region in which a magnetic
| force can be detected. Ever seen a police car on the motorway? Everyone
| within 100 yards drives exactly at the speed limit. the police call this a
| bubble or zone of legality. The zone isn't composed of anythig but you can
| "feel the force".

It is composed of something called "fear".

Sod that, I overtake the buggers. Never been pulled yet.

--
Clint Sharp