Hi
I know it's possible to buy EMF field detectors to detect fields created
by electric current, but is it possible to buy a detector to assess the

strength of non-electrical magnetic fields. The closest I've been able to
get with this is by monitoring the change of a digital compass when it
comes into contact with a field. I can find no precision instrument to do
this. Does anybody know if one is available?
Thanks
Regards,
Pan

Just wondering, how would you have a non-electrical magnetic field? Any
magnetic field would have some electrical properties. Unless I am missing
something

to
do
I'll second that. Even the magnetic field from e.g. a bar magnet comes from
moving charge.
Pan, are you looking to detect only 'dc' components of magnetic fields, like
from our planet, or a piece of loadstone sitting on a table? In fact, if
you flesh it out a bit more what you're after, it may help.
j

to
do
I understand that the magnetic and electrical fields are exclusive and
different. See Faraday's and Maxwell's laws.
A non-electrical magnetic field would be one associated with a material
with a magnetic or paramagnetic property.
An electrically induced magnetic field is one created by moving charges
(current in a coil)

You understand incorrectly- however, at DC or low frequency AC, the electric
and magnetic fields can be considered independently. I suggest that you look
at Maxwell's equations again (Faraday is imbedded in these).
As to non--electrical field - this has nothing to do with the magnetic or
paramagneticl properties of the medium.

My understanding of electric and magnetic fields being exclusive and
different phenomena is 100% correct.
First, the point of referencing Faraday's and Maxwell's laws relating
magnetic field to electric fields was that within those Laws, magnetic
fields and electric fields 1) exist exclusively as distinct physical
phenomena, and 2) must exist distinctly, exclusively and different
phenomena, in the equations for those equations even to exist
mathematically, i.e., electric and magnetic fields exist separately,
exclusive and different phenomena.
One look at the equations, and you see two entities. That means there are
two entities, not one of differing form.
To shut down any further discussion of them not being separate and
independent fields, look at Gauss' and Coulomb's laws. Electric-field-only
laws, and for Gauss, also a magnetic-field- only law. Separate and distinct,
exclusive and different.
Yes, one phenomena may create the other - BUT ONLY if there is relative
motion. And for one to create the other, that requires -and means - that
they are exclusive and different fields, not one phenomena.
a)
http://physics.usc.edu/~bars/135/LectureNotes/EMinduction.html
"Electric currents or moving charges create magnetic fields
Magnetic fields exert forces on moving electric charges"
separate and distinct - one will create the other if MOVING -
NOT MOVING - separate and distinct, exclusive and different.
b) Faraday's Law rests on their being exclusive and distinct fields (and
note that there is no frequency limit in the equation.)
Faraday's law (M. Faraday)
The line integral of the electric field around a closed curve is
proportional to the instantaneous time rate of change of the magnetic flux
through a surface bounded by that closed curve; in differential form,
curl E = -dB/dt,
As Faraday's Law states, there are independent and separate, exclusive and
different fields -
Note the words "electric field" and "magnetic flux through a surface"
(Phi º, i.e., magnetic flux is the product of the average field times the
area the MAGNETIC FIELD penetrates)
The two exclusive and different fields must exist for the equation to be
valid. And it is valid.
c) Maxwell -
http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Electromagnetism/20010329163249.ht
same criterion for the equations to exist - the electric and magnetic fields
must be exclusive and different, as indicated in the various equations
FWIW -
Note that what you posted contradicts itself
1)

you are speaking of the [magnetic] field.
Your statement is not incorrect - however, your statement admits that the
magnetic field exists exclusively and different from any electric field.

(That is because they ARE independent at all frequencies. There is no
frequency component in Faraday's and Maxwell's Laws. You may be confusing
inductance with magnetic field, or possibly the E, B and H vectors?)
----------
For the experimental proof usually used in basic physics lab:
Is there a magnetic field in a capacitor? A magnet does not move near a
charged capacitor. A magnet moves near another magnet. The magnetic fields
exist, and are not affected by the charge in the capacitor
Is there an electric field in a stationary magnet? An electric field does
not change near a stationary magnet. And electric field changes near a
charged ball. The electric fields exist, and are not affected by the magnet.
The two fields exist independently, and are exclusive and different
phenomena.

I understand that Einstein wrote a paper showing that what we consider to be
magnetic phenomena actually arise from relativistic consideration of
electric phenomena. All there are are electric fields. Magnetic fields are
a handy modeling concept. How would you reconcile this with your 100%
different hypothesis?

material
charges
I understand that all magnetic fields are due to charge in motion.
Ferromagnetic, paramagnetic, diamagnetic, and ferrite materials all have
magnetic field resultant from moving charge, e.g. electron orbits, electron
spin, nucleus spin. Can you provide an example of a magnetic field that
arises from other than charge in motion?
j

be
I have not seen that paper - however, he had written several papers trying
to marry the several forces into one unifying theory, and some papers were
incorrect and discarded.

Your argument is circular - You could have just as well said that electric
fields are a handy modeling concept, used to describe magnetic fields. Both
magnetic and electical fields are artificial concepts use to describe
observed phenomena.
Think of force - force does not exist except as a concept used in
mathematics to predict behavior. You cannot see it, hold it, or observe it
directly.
Besides, electric and magnetic fields each have distinct different
characteristics
How would you reconcile this with your 100%

Your logic is improper by implying a fact you stated is proven; thus your
conclusion is in error - I do not accept one of your "facts", i.e.,
"Magnetic fields are a handy modeling concept. "
Thus I do not accept your implied conclusion that my statement needs
reconciling.

electron
Once again, you have used the same faulty logic. No, all magnetic fields
are NOT due to charge in motion. Your second statement is correct - the
magnetic fields of most naturally occuring materials are derived from moving
electrical charges.

Can you provide an example of a moving electical field that does not create
a magnetic field? Coherent spin manipulation in strained semiconductors?
All magnetic fields listed in the electromagnetic equations do not require
an electric field. They have to be separate and distinct entities to exist.
1) You can check most basic physics texts to verify the difference between
the two kinds of fields:
The difference between a magnetic field and an electrical field is that
the magnetic field is a dipole field (That means that every magnet must have
two poles.) and the electrical field is a monopole field (an electrical
field of either a positive (+) or negative (-) charge can stand alone.
2) And they are defined as distinct in the fundamental laws of
electromagnetics. That alone is proof enough that they are distinct.

to
It was his 1905 paper on special relativity, 'On the Electrodynamics of
Moving Bodies'.
http://www.fourmilab.ch/etexts/einstein/specrel/www /
"What led me more or less directly to the Special Theory of Relativity was
the conviction that the electromotive force acting on a body in motion in a
magnetic field was nothing else but an electric field."
A. Einstein (1952), from a letter to the Michelson Commemorative Meeting of
the Cleveland Physics Society, quoted by R.S. Shankland, Am. J. Phys., 32,
16 (1964), p35.
http://www.ph.unimelb.edu.au/~dnj/teaching/160mag/160mag.htm
"WHY DO MAGNETIC FORCES DEPEND ON WHO MEASURES THEM"
There's an example to look at here if you scroll to the Minkowski diagrams
at the bottom. The remainder of the page is also on the topic.
I'm not familiar with argument along the lines of 'the equations show two
entities and therefore the two are exclusive and different'. I would put
forth the entity a (a=F/m) and the entity dv/dt (dv/dt=ds2/d2t). I don't
think there is anything preventing E and B from being two considerations of
the same thing (e.g. if some 'higher' relationship constrained the two or
if something GUT-esque came along) even though they are commonly shown by
us now as two different equations in certain formations.
You gave a link, presumably to provide examples of magnetic fields
originating from other than charge. Checking that link I saw no mention of
any origins of any magnetic fields. Was that the link you intended to give.
j

http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Electromagnetism/20010329163249.ht
------------
Moving charge- i.e current- produces a magnetic field which if varying with
time, produces an electric (potential) field as per Faraday. If the
varying magnetic field cuts a wire, it doesn't cause a charge "flow" or
current in the wire, but merely a non-zero electric field in the wire- and
this doesn't necessitate a current or charge flow. To be pedantic, a
voltage is induced- not a current - and this voltage will exist whether or
not a current (or even the wire) exists. It is common but incorrect usage
to say that a current is induced. Your second semester physics experiment
detected the induced voltage by measuring a current produced by the voltage.
Fair enough.
----------------

----------
The relationships in Maxwell's equations are not dependent on dipoles or
monopoles.
curl E =-di(B)/di(t) (di to represent partial derivative)
curl B= mu*J = permeability{conductivity*E +permittivity*
di(E)/di(t)}=mu*(Jc +Jd)
These imply coupling.
-------------------

------
With the exception of not using partial derivatives, we have been using
dx/dt or whatever, correctly. ? Faraday's law is applicable at an instant.
What is your point here?

I found something as I finished cross-checking defunct terms in my already
completed closing post (some info other than the subject of this day's post)
so I top posted the following FYI -
"Units of the electric field = [Newtons / Coulomb]"
"Units of the magnetic field = [Tesla] = [Newton second / Coulomb / meter]
"
Different units.
I also noted that units of magnetic field _strength_ are amperes/meter.
(BTW - I love it how SI creates a strength unit without a unit of force,
and using their chosen base unit of amperes, gives us the coulomb as
ampere-seconds.
Only in SI do we have strength without any unit of force and charge
measured in seconds of charge flow.
Worse, we told them it would happen.)

-------
That is true but, as I didn't need to use full blown EM theory in dealing
with power systems (even lightning surges) or machines, I simply didn't keep
up with this. As to proofs- I actually do not recall any non-vector proofs
or usage and I have long lost my old copy of Jackson. Ardley uses vector
forms as well as matrix expressions and tensors in some cases.

--------
I dropped oerstads, abamps, etc, very shortly after being introduced to
them. Now when I see "Gauss" I have to mentally convert it to SI. It was
either the late 50's or early 60s that I was converted to the metric/SI
system. However, part of the trend in SI was/is to honour the dead by
renaming units -ie. Tesla instead of Weber/sq.meter or mho to Siemen when
the original units were actually more descriptive.
I find that the metric/SI units are easier than the English units in dealing
with mechanics or electromechanics.
I apologise for one statement that I made which implied exactly the opposite
of what I intended. Certainly I accept Maxwell's equations at all
frequencies. It is circuit theory which is an approximation to full blown EM
theory. This is good but has limitations and is what has been called a
"quasi-static approximation".

--
Take care. It's been good to talk with you and exercise my brain as well as
being a contrary old fart (a category I have earned ).

My apologies if I didn't make what I wanted clear in my original post. I
already have a meter here for detecting EMF fields given off by AC
electric, but I had no way to pick up naturally occurring magnetic fields
like those given off by standard magnets or audio speakers. So I was
wondering if it was possible to buy a detector for picking up these fields
as well.
It seems from what I've read here that this type of magnetic field is
actually based on DC electrical properties and can be detected by a DC
Gaussmeter. So I'll try and get hold of one of those :) Thanks to all of
you for your help.
Regards,
Pan

to
do
look around for a Magnetometer... i believe the navy uses them to locate
submarines and mines.
i have a small one that indicates the magnetic charge of a tape head

On Sat, 17 Dec 2005 01:11:38 -0500, TimPerry wrote:

Thanks for the suggestion. I'll look out for one of those too :)
Unfortunately, from what I can tell, both items do seem pretty
expensive :)
Regards,
Pan

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