PREAMBLE
Earth
Magnetism or E.M is one of the oldest themes
in the Earth study. The world scientists are researching, debating
about the same theme for several decades; I assume that there is not
only one but some of them even dropped it.
I am neither going to deny the settled
theories about E.M nor to make the Geomagnetism up-side-down, but
consider the E.M as one constituted by 2 major parts. The ‘’part
I’’ mainly presents the contributions from the charges at sea surface and
land surface. The other one is a massive part that contributed by external magnetic
inducers such as Van Allen belt, Moon and atmosphere; a shocking extra chapter is the magnetism at The Poles.
The mechanism in magnetic inducement of
E.M is rather complicated and likely to be ruled by some principles
that had not been mentioned so far; each spot on the Earth is
different to any other.
The very special paradox is that ‘’land
charges versus sea surface charge in contributing to the E.M whilst
they both are moving together with Earth’s rotation’’. Although
land charges and sea surface charge are influenced by external
movement, I do keep them in a separate part (Part I) for a better
discussion.
Actually I leave what happen inside the
Earth as the stuff of a conservatory; just add something on the
settled basis with some effects on Earth surface and from sky.
Many scientists assume that the
astronomic objects may contribute several per cents in the E.M. In
this book, I argue that the contribution from those might go beyond
any previous prediction and certainly it must not be such tiny as
assumed by those scientists…
E.M is a giant theme like the huge size of the Earth. I am
capable and proud to interpret some of the information that compiled by many
scientists in history and especially in about a century time.
Furthermore, like any other semi-empirical study, this book
presents some latest E.M data and I analyse them with my own view. On some
aspect, this book is more likely presenting a discussion by which I contribute
my own view to a theme that researched by tens of scientists in the world.
Like any other book, this is compiled with reference to many
books as well as researching reports from many scientists in the world. The
knowledge from electricity to atmosphere, from math to physics; all of them are
referred to facilitate the research.
The Earth rotation is definitely to suggest us that E.M is
created by the rotation, or the Earth is viewed as an electromagnet. I trust
that the E.M must look alike a normal magnet if we eliminate all external
compositions (but I don't attribute the astronomic power as reason for the gap between North magnetic pole and the geometric one).
The above assumption has been the subject of much and long study, particularly by S.J. Barnett, who has shown that a piece of iron may be magnetized by rotation.
The above assumption has been the subject of much and long study, particularly by S.J. Barnett, who has shown that a piece of iron may be magnetized by rotation.
In 1900, Sutherland suggested a possible cause of the Earth
Magnetism the rotation of an electrostatic field within the Earth –a positively
charged core and a negatively charged crust, or vice versa.
The later analysis made by Bauer in 1922, using improved
data based on modern observations, gave approximately the same result.
Sutherlands, Bauer and Swann suggested that we may have to
look for some slight but fundamental modification to those accepted laws.
(Magnetic storm) it was recognized that the more severe
magnetic disturbances occur at practically the same time all over the Earth,
and further comparative study of abrupt beginnings and sharp turning points
indicated strict simultaneity.
The world scientists keep researching the Earth as well as E.M
at all time. The followings are some information in brief about the science
achievements:
-Temperature at Earth’s inner core boundary: by measuring
the melting point of iron at high pressure (about 2.2 million times more than
normal pressure on Earth surface) in laboratory, the scientists drew a result
to calculate the temperature now estimated at 6,000 0C (about 10,800
F), that’s as hot as the surface of the Sun?
-Earth’s inner core is solid, while its outer core is molten
or loose then crust and mantle above the outer core. Along with Earth’s spin
they create the magnetic field?
X
X X
Before any further discussion about E.M, we should not
neglect the following from an important book ''TERRESTRIAL MAGNETISM''.
Quote:
In the previous centuries,
the XIX and XX, human being had carried out a series of attacks to the Earth
Magnetism, the questions are: What it is, What caused it, What cause it to
change. Many leading physiscists, mathemeticians joined in those attacks. Many
theories, one after another had been advanced then withdrawn if it was found
inconsistent with some of the observed facts.
1/They are inadequate or
inconsistent because:
-Can fit well with quality
but can’t do with quantity.
-Can fit well with primary
stage but can’t do with the next when our knowledge is improved.
2/The advances in other field of science have been employed:
-Cathod rays, electronic
theory of matter.
-Constitution of the Sun.
-Earth interior.
3/Gilbert’s conception: Earth is a great magnet uniformly magnetized about the Earth own rotating axis. This theory is discarded afterward when the high temparature inside the Earth is recognized by then some material is demagnetized in such high temparature condition.
4/Under high pressure: properties of some matter in great pressure may be materially different from those observed in normal condition. Susceptibility to magnetization is one of those properties. Some geophysicists suggest that the Earth’s inner core is composed by almost entirely Nikel and Iron and a possibility of susciptibility of magnetization in spite of high temparature, because of enormouse high pressure. Some magneticians are inclined to work further to consider The Earth as a giant magnet.
5/ Electric currents flowing around The Earth: When it seemed clear that the conception of the Earth as a permanent magnet could be sustained, the idea was advanced that the Earth magnetic field might be due to electric currents flowing about the Earth, either below the surface or in the atmosphere-the Earth an electromagnet.
6/Three portions constituting the E-magnetism: The mathematical analysis of the Earth magnetic field, according to the method devised by Gauss and extended by Neumayer and Peterson (1891) and Schmidt (1896), indicated that:
-A portion of Earth
Magnetism, perhaps one-fortieth, could be referred to forces outside the
Earth.
-Another small portion
to vertical electric currents.
-But by far the larger
part to a system of force within the Earth.
A new analysis made
by Bauer in 1922, using improved data based on modern observations, gave
approximately the same result. He reached the conclusion that for a
satisfaction representation of the observed data it is necessary to recognize
the existence of an internal magnetic system constituting about 94 per cent
of total field, with an external system and a non-potential system each
amounting to about 3 per cents.
A comparison of his
results with those previously obtained for the epochs: 1842 and 1885 indicated
that the intensity of magnetization of the Earth had been decreasing during the
80 years at an average annual rate of one part in 1,500; a rate of loss
which it is hard to reconcile with the age of Earth and the present intensity
of magnetization unless we suppose that there have been also periods of
increasing intensity.
7/ E-Magnetism caused
by Earth’s rotation: The idea of Earth as an electro magnet naturally suggested
the possibility that its magnetism may be caused by its rotation. This
possibility has been the subject of much study, particularly by S.J. Barnett,
who has shown that a piece of iron may be magnetized by rotation, though the observed
effect was much too small to account for Earth Magnetism. In 1900, Sutherland suggested as a possible
cause of the Earth Magnetism the rotation of an electrostatic field within the Earth
–a positively charged core and a negatively charged crust, or vice versa.
8/ Electronic theory
and Sutherland: The development of electronic theory of matter, with the atom
consisting of a positively charged nucleus surrounded by negatively charged
electrons, led Sutherland to suggest that if for some unknown reason, connected
perhaps with gravitation, the negative charge of the atom is farther from
centre of Earth than the positive charge by only 4x10-9 cm, it would
account for a magnetic field comparable with that of the Earth. When the
electronic theory had been more fully developed and Sutherland’s hypothesis
submitted to further test, it was found to be untenable either qualitatively or
quantitatively.
Failing to find a
satisfactory explanation to the Earth’s magnetism on basis of the known
properties of matters and accepted laws of electrodynamics, Sutherlands, Bauer
and Swann suggested that we may have to look for some slight but fundamental
modification of those accepted laws, possibly as regard the mutual
attraction and repulsion of moving positive and negative electrons, similar to
a suggestion of Lorenz regarding the cause of gravitation. Indeed there seems
to be growing a belief that gravitation and terrestrial magnetism are very
closely allied and probably to be traced to a common origin.
9/ Atmosphere
electric & Earth currents: In view of difficulties in the way of a
direct solution of the problem of the cause of Earth Magnetism, the magnetism
researchers have turned their attention to a study of its variations and their
correlation with associated phenomena, such as atmospheric electricity, Earth
currents, aurora, sun spots, solar radiation, in the hope that the cause of
variations may be discovered, and that in that way light would be thrown on the
main problem. In particular, magnetic storms, those irregular disturbances of
large amplitude and comparatively short duration, have been the subject of much
study.
It frequently happens
that the occurrence of magnetic storms and auroras coincides with the presence
of large spots on the sun, and this naturally has led to attempts to trace a
causal relationship. It was soon seen that a direct magnetic effect by the
sun was out of the question, because of great distance. With the
development of the idea that the Earth’s magnetism may be caused by current of
electricity, different forms of electric discharge emanating from the sun were
successively put forth as the cause of observed terrestrial phenomena, the
theories advanced keep pace with the development of our knowledge of electrical
discharges in vacuum.
The correlation between
magnetic storms with sunspots, although very satisfactory when based on yearly
average, leaves much to be desired when individual cases are considered. Thus
severe magnetic storms sometimes occur when no large sunspots are visible,
and on the other hand a sunspot is not always accompanied by a magnetic storm.
Large magnetic storms always follow each other at an interval approximating the
time of revolution of the sun and such reoccurrence has been traced with
several rotation periods, not every recurrence is accompanied by a sunspot,
however.
10/ Maunder
hypothesis:
To meet these conditions, Maunder advanced the
hypothesis:
-The solar activity
which gives rise to magnetic disturbances on the Earth does not act equally in
all directions but along narrow well-defined streams, not necessarily truly
radial.
-These streams arise
from active areas of limit extent.
-These active areas
are not only the source of our magnetic disturbances but are also the seats of
formation of sun spots.
-These areas can be active
both before a spot has formed and after it has disappeared.
Birkeland, Arrhenius,
and Normannd agree to consider aurora as a luminescence produced by the
absorption of cathode rays in the upper atmosphere and attracted toward the Earth
magnetic poles. Birkeland, who devoted many years to the study of auroras,
advances a theory that cathode rays from sun can set up electric currents in
the atmosphere which in turn give rise to secondary cathode rays. He supported
his theory by the production of artificial auroras in laboratory, about a
magnetized steel ball in a tube of rarefied air exposed to cathode rays.
11/ Sun’s electrified
particle streams:
If magnetic
disturbances on the Earth are to be ascribed to streams of electrified
particles shot out from the sun, we should expect to find a disturbance
occurring first at the part of the Earth first entering the stream and later at
other places as they in turn entered the stream, as a result of the combined
motion of the Earth in its orbit and the sun about its axis. From the time of
the earliest comparison of photographic records from widely separate
observatories, it was recognized that the more severe magnetic disturbances
occur at practically the same time all over the Earth, and further comparative
study of abrupt beginnings and sharp turning points indicated strict
simultaneity, the departures therefrom being ascribed to errors inherent in the
time measurements, so that the more accurate determination of the time
of occurrence of such salient features was suggested as a method of determining
differences of longitude.’’
Unquote
The latest document for the same theme-the Earth’s magnetic
field, is one from a French Scientist; I would like to cite here a short
excerpt from his argument:
Quote
THE ORIGIN OF THE
EARTH’S MAGNETIC FIELD: FUNDAMENTAL OF ENVIRONMENTAL RESEARCH? (Emmanuel
Dormy-MHD in Astro-and Geophysics, Department De Physique, LRA, Ecole Normale
Superieure-France.)
The origin of The
Earth’s magnetic Field is a long-standing issue, which has captured attention
of many reknown scientists. If William Gilbert, Andre-Marie Ampere, Rene
Descartes, Edmond Harlley, Kart Friedrich Gauss, Lord Brackett and many others
who contributed to the development of science, have worked on this problem, it
is mainly because it related to a very important issue of very critical
importance: navigation at sea. This is not so true any more, now that
satellites provide the precise latitude and longitude without the need for us
to rely on Earth’s internal magnetism. Yet the question of origin of Earth’s
magnetism is so natural that it is still an object of very competitive
research. Nobody can ignore that the compass needle points toward the North,
and it is a bit irritating that we still can’t not offer a complete physical
understanding of why it is so. The problem therefore becomes an active field of
fundamental research in which significant progress has been made in the last
few years using combined theoretical, experimental and a numerical approach. By
its very nature, the problem is interdisciplinary
and lies at the interface of physics, geophysics and applied mathematics. This
problem has recently received considerable attention in the press because of
concern of a possible reversal of polarity of the Earth’s magnetic field in the
near future. Considering that we risk seeing our planet unshielded from solar wind,
understanding the field generation mechanism again appears to be a societal
concern and a legitimate goal of environmental research.
’THE ORIGIN OF EARTH’S MAGNETIC FIELD
When the Earth formed
in 4.5 billion years ago, heavy elements concentrated at centre, as result 3000
km below our feet lies the largest of our planet’s oceans: the core of liquid
iron (mixed with traces of light elements), a sphere of 3400 km in radius. As
the pressure increases towards to the heart of the Earth, the iron solidifies
and we find a solid inner core, which occupies a volume of 1200 km of radius.
It is the metallic core that the magnetic field of the Earth originates.
Temperatures at such depth are above 3000 degrees K and thus well above Curies
point (at which metal loses its ferromagnetic properties). A magnetic field can
therefore only be sustained if electrical currents circulate in this ocean of
liquid iron. However, Ohmic dissipation would suppress any unsustained
electrical current in the Earth’s core...’’
Unquote
About the same theme, we can’t ignore the following that
cited from an academic literature of science in United Kingdom. At the first
page we find right away:
Quote
We have gone through many theories but not the following
combined theory which is most read at present time:
‘’The Earth and most
of the planets in the Solar System, as well as the Sun and other stars, all
generate magnetic fields through the motion of highly conductive fluids. The Earth's field originates in its
core. This is a region of iron alloys extending to about 3400 km (the
radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core. The motion of the liquid in the outer core is driven by heat
flow from the inner core, which is about 6,000 K (5,730 °C;
10,340 °F), to the core-mantle boundary, which is about 3,800 K
(3,530 °C; 6,380 °F). The pattern of flow is organized by the
rotation of the Earth and the presence of the solid inner core.
The mechanism by which
the Earth generates a magnetic field is known as a dynamo. A magnetic field is generated by a feedback loop: current loops
generate magnetic fields (Ampère's
circuital law); a changing
magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert
a force on the charges that are flowing in currents (the Lorentz force). These effects can be combined in a partial
differential equation for
the magnetic field called the magnetic induction equation:
...where u is
the velocity of the fluid; B is the magnetic B-field; and η=1/σμ is the magnetic
diffusivity, a product of
the electrical
conductivity σ and
the permeability μ. The term ∂B/∂t is
the time derivative of the field; ∇ 2 is the Laplace operator and ∇ is the curl operator.
The first term on the
right hand side of the induction equation is a diffusion term. In a stationary fluid, the magnetic field declines and any concentrations
of field spread out. If the Earth's dynamo shut off, the dipole part would
disappear in a few tens of thousands of years.
In a perfect conductor
(σ=∞), there would be no diffusion. By Lenz's law, any change in the magnetic field would be immediately opposed by
currents, so the flux through a given volume of fluid could not change. As the
fluid moved, the magnetic field would go with it. The theorem describing this
effect is called the frozen-in-field theorem. Even in a fluid with a
finite conductivity, new field is generated by stretching field lines as the
fluid moves in ways that deform it. This process could go on generating new
field indefinitely, were it not that as the magnetic field increases in
strength, it resists fluid motion…’’
Although I am writing purely about external influence, I
must make an unforgivable mistake if I don’t mention these issues:
-The gap between Earth’s rotation axis and magnetic pole: This
issue will be re-compromised in the conclusion of this book. However, one of
hypothesises about the origin of Earth Magnetism presumes that the ‘’yolk’’ of
the Earth, which induces the Earth Magnetism, used to be together with Earth’s
rotation axis but shocked by a huge meteorite then turns North side South. The
‘’turn’’ has not been perfect and leaves the North Magnetic pole far from
geometric North pole (about 110-170). By that author, the
collision with the huge meteorite made a very serious disaster to the living in
Dinosause Era, when all the Dinosause dead.
-The deviation and magnetic-longitude of ‘’0’’ deviation.(Magnetic
susceptibility of material).
The relevant documents may build a huge pile; we can’t read
every one of them but the following magazine- The GEOMAGNETISM-Magnetic Model
and Navigation. The paper is to affirm that ‘’the study of geomagnetism is one
of oldest geophysical sciences. Geomagnetic fields have been observed and been used
from ancient time.’’ That paper also emphasizes that the magnetic compass
needle does not point toward the North Magnetic Pole, but in the direction of
the magnetic field line-horizontal composition-at the place where the compass
is located.
On the scope of International cooperation in research, the
paper introduces World Magnetic Model (WMM), a joint product of the United
States National Geospatial Intelligence Agency and United Kingdom Defence
Geographic Centre. This model is used by many giant and important bodies such
as U.S Department of Defence, NOAA, U.K ministry of defence, NATO,
International Hydrographic Organization (IHO).
The paper is interesting and to be one of viable information
sources for the author of this book.
The latest information from a science magazine
is the model of some French scientists.
Image 7/F-Earth Magnetism
produced in the core
''The Earth core is supposed to be filled with molten
Magnesium since Earth’s violent birth. The flow or move of the molten in Earth
core is to produce Earth Magnetism.''?
Anyhow, those scientists must satisfy themselves as how the magnesium
can be mixed together with iron, even if the molten magnesium is found in
there.
PART I
Some viable concepts and
The Sea vs Land contributions
to Earth Magnetism
Chapter I
VIABLE RELEVANT CONCEPTS
Nowadays, the quantum theory is the first and the most that
catch the attention of the people in the world. Nonetheless, we should
recognize that the physics can’t be just bracketed in quantum, and so we got to
look backward some centuries when we can find W. Coulomb, A.Ampere and the two others
J.B.Biot and F.Savart.
I-Static Electric Charge and Coulomb:
This is the first we inspire when discuss about Earth
Magnetism, the subject is attached to a scientist who discovered electric
charge: W. Coulomb.
His rule is simply expressed in a formula for the force (F)
between the two charges:
F=ke*q1*q2/r2
Or
=ke*q1*q2*r-2
Where q1 and q2 are values of charges, each can be either (-)
negative or (+) positive. The distance between the two is ‘’r’’ and the Coulomb
constant ‘’ke’’ is depending on the media between the two.
ke=8.99*109 N.m2.C-2:
Coulomb constant for the normal environment or vacuum between the two charges. The
force is found to be negative (-) when either q1 or q2 is negative; to be
positive (+) when both of them are positive or negative; this is quite a law in
math and it demonstrates the wise of force ‘’+ push’’ or ‘’- pull’’.
Portrait of
Charles-Augustin de Coulomb
Charles-Augustin de Coulomb was an eminent French physicist.
He formulated the Coulomb’s law, which deals with electrostatic interaction
between electrically charged particles. The coulomb, SI unit of electric
charge, was named after him.
We are considering ‘’ke’’ for the media of large scale
and complicated, therefore we should give out some assumptions before any
problem.
Some more about moon-earth relation and calculation are debated
in the ‘’Moon charge and E.M’’ of this book.
II-A. Ampere:
The second scientist we inspire is A. Ampere, he is a great
scientist but simply his rule should be taken as: total charge in Coulomb
transported through a point within a unit of time (second) is to make current
value one Ampere.
(Portrait of André-Marie
Ampère)
André-Marie Ampère (1775-1836) is a French Physicist and
Mathematician; He worked at the beginning of the 1800s in Paris, France. He
used his mathematical and statistical skills to observe and measure natural
occurrences that had been discovered by other European scientists. He went on
to produce complete proof of the relationship between electricity and
magnetism. He also developed a new way of classifying chemical elements. Amp (Ampere)
or his name is given to basic unit of electricity.
With the above concept of electric current, an instant of the
5 different charges moving through a point in 5 seconds can make an average
current in that interim as following:
2 Coulombs in 1st second;
3 Coulombs in 2nd second;
1 Coulomb in 3rd second;
2 Coulombs in 4th second;
4 Coulombs in 5th second, can make a current of:
I = (2+3+1+2+4)/5=12/5=2.4 A
Figure 1/I-Electric
current & magnetism around
As soon as an electric current is created, a magnetic field
is established around it.
III-Biot-Sawart laws:
In physics, the momentum as well as the ‘’particle spin’’ is
considered as the most interesting subject. Let’s leave the modern physics and
work with these two scientists.
Jean Baptiste Biot – a
French scientist (1774-1862)
Felix Savart-a French
physicist (1791 -1841)
Those two French physicians are known as inventers to the
law that named after the both, the Biot-Savart about electromagnetism.
1-Biot - Savart law: The kernel of the law is to say
that a charge motion is to make magnetic field. A point ‘’P’’, at a distance ‘’r’’
from a conducting wire where the charge moves in, is in a magnetic field which
can be calculated as following:
Where dB is additional magnetic field contribution induced
by the current ‘’I’’, which is created by the directional move of a charge
‘’q’’.
Figure 2/I-A charge
move and its magnetism contribution to point P.
And ‘’ds’’ is a small segment of wire, both ‘’ds’’ and ‘’ȓ’’
are respective vector units of wire length and distance from the wire to ‘’P’’;
and product of those is dB -an outward vector or the vector that comes toward
reader as following figure.
µ0 – permeability coefficient of environment, is
4π
* 10-7 in normal air or vacuum.
2-Biot-Savart problem of many moving charged points:
Our discussion is not the first but is the most interesting application
of Biot-Savart law, which will be applied to almost every issue in this book. Instead
of momentum and spinning, we work with charge and orbiting. The following is an
excerpt from a manual on web.mit.edu.com (Mit. University web).
Quote:
The magnetic field due to 30 charges moving in a circle at a
given observation point. The position of the observation point can be varied to
see how the magnetic field of individual charges adds up to give the total
field.
In the above figure (9.1.11), we show an interactive Shock
Wave display that is similar to that in figure 9.1.10, but now we can interact
with the display to move the position of observer about in space. To get a feel
for total magnetic field, we also show a ‘’iron filings’’ representation of the
magnetic field due to these charges. We can move the observation point about in
space to see how the total field at various points arises from the individual
contributions of the magnetic field of to each moving charge.
Note, however, that since a point charge does not constitute
a steady current, the above equation strictly speaking only holds in the
non-relativistic limit where v<<C, the speed of light, so that the effect
of ‘’retardation’’ can be ignored.
The result may be readily extended to a collection of N
point charges, each moving with a different velocity. Let the ith charge qi be located at
(x,y,z) and moving with velocity v, using the superposition principle, the
magnetic field at P can be obtained as:
Unquote.
IV-Major historic notes:
This book is not written about industrial magnetism but the
subject is vital to the contemporary life, therefore the following note must
benefit the readers in general. On the other hand, some reader can’t get
through this book without reference back these notes.
The above figure illustrates how a direct current induces the magnetism
during flows through a coil.
1-Magnetic field
intensity: This is defined as the ratio between the max magnetic flux
density of a circuit to the permeability of free space.
H=B0/µ0
The magnetic intensity depends on the geometry of the
circuit and the conduction current, not on the medium.
The total magnetic field in a magnetic material is due to
the conduction current in the external circuit and the microscopic current
developed in the material.
B=B0+ µ0*M
2-Field strength (H):
Definition: It is the force experienced by a unit north pole
at a point in a magnetic field
H=F/m
Where F is the force, m is pole strength.
-If the field lines are more, then H is high and vice versa.
-Thus, the closer to the pole, the higher strength of
field.
Nowadays, magnet is applied in almost every equipment or even
toy. The power of U-shaped magnet is known to everyone who is experienced with
machinery work.
3-Magnetization:
a-Magnetic domains in an
un-magnetised bar point to random directions.
b-A bar magnet is brought near
the un-magnetised bar.
c-The magnetic domains point in the same direction,
producing magnetism. N or S poles of adjacent domains cancel each other out.
d-The atomic magnets at both ends are free. This produces N
and S poles at the ends.
e-The atomic magnets at the ends tend to fan out due to
repulsion between the like poles.
The magnet and its force applied in industry are not magic;
they are available in every material and everything, their force is null
because every elementary magnet in there points to different directions or even
one eliminates the other. The external magnetic force helps a certain bar in
its adjacent area to re-direct every elementary direction and make a force of
their total.
4-Magnetic Equivalent
Circuit:
Magnetic Field
Intensity (H): the amount of field force (mmf) distributed over the length
of the electromagnet. Sometimes referred to as Magnetizing Force.
Magnetic Flux Density (B)-The amount of magnetic
field flux concentrated in a given area.
Where N-numbers of turns of coil; i-current in the coil;
H-magnetic field intensity; l-mean length of the core.
Relation between B and H:
The magnetic field intensity, H produces a magnetic flux
density, B everywhere it exists.
B=µH (weber/m2) or Tesla
B=(µr/µ0)H(w/m2) or T
µ: Permeability of the medium.
µ0: Permeability of free space=4π.10-7
wbA.t.m
µr=µ/µ0 relative permeability of
medium.
Magnetic Flux Φ
-Unit
for flux is ‘’weber’’
-The
definition of 1 weber is the amount of flux that can produce and induced
voltage of 1 volt on a one-turn coil if the flux reduced to zero with uniform
rate.
This
concept is also defined as following: It is a measure of magnetic field in a
certain medium. In simple term if the magnetic field has to pass through a
certain medium, it will always travel as ‘’flux’’ lines (flux lines are
imaginary, but continuous lines travelling from North pole to South pole of a
magnet. Its units are Weber.
Magnetic Flux Density B
-Unit
for magnetic flux density is Tesla.
-The
definition of 1 tesla is the flux density that can produce a force of 1 Newton
per meter acting a conductor carrying 1 ampere of current.
Magnetic Field Strength H
-Unit
for magnetic field strength is Ampere/meter.
-A
line of force that produce the flux.
Earth’s Magnetic intensity in history and now (an
excerpt):
The above note is cited as some information about the
Earth’s magnetism in history and now. Definitely Humphreys does not fabricate the
graph, and he draws it with facts that found in researching. The question is
‘’steady decay’’ now and then?
V-Major Features & compositions:
1-E.M polarity: at present, south magnetic pole is
nearly coinciding with earth north geographic pole, that’s why magnetic compass
north hand always points toward North.
Figure-3/I-Earth
Magnet with zero-deviation.
The above image is set with assumption that magnetic
deviation is ‘’nil’’, and South magnetic pole is on North geographic pole.
2-Earth Magnetic field in different coordinates:
The following is an excerpt from manual of Bremen University:
3-Earth Magnetic field compositions:
Earth Magnetism or E.M is contributed by several magnetic
inducers, we are going to discuss about someone and not the whole. Unlike
traditional way, our way is to start from inducers such as charge on continent,
sea surface charge and Moon charge. Therefore we got to denote each magnetic composition
with a number attached to a symbol ‘’Δ’’ such as Δ(1) or Δ(2), except B(e)
which is induced by inner rotor of the Earth as well as local man-made source.
B(e) is also denoted as Δ(7), the only one composition which has undefined
direction and left as non-directional quantity, while all the rest are
directional.
-Positive charge on land contribution: Δ(1),
note that positive as well as negative charge is everywhere, but we do not
consider every one as it is but with massive quantity as representative of each.
Therefore a continent is positively charged in general. Direction of Δ(1)
will be defined in its problem, the land charge contribution in chapter II of
part I-‘’sea surface charge versus land charges’’.
-Negative sea surface contribution: Δ(2), unlike continental
surface which is positive, the sea surface is homogenous as only one electrode
and always negative. The direction of this composition is defined in its
problem, chapter II of part I.
-Van Allen belt contribution: Δ(3), Van Allen belt and its
companion, the plasma sphere, are not just making a shield to protect the
Earth, they are charged and to contribute to E.M. The direction of their
contribution is defined in the problem in chapter I of part II.
-Negative moon’s hemisphere contribution: Δ(4),
the Moon primarily is assumed as neutral with 2 hemispheres of 2 opposite
charges. Each hemisphere is inducing magnetism to Earth different to the other.
The direction of this quantity is defined in its problem in part II.
-Positive Moon’s hemisphere contribution: Δ(5),
the shined hemisphere of Moon is positive as losing electrons under solar wind.
It induces magnetism to Earth and its direction is defined in its problem in
part II.
-Contribution of total charge of Moon: Δ(6),
the above mentioned problems are considering Moon as neutral of 2 opposite
charges, but in reality the total of those charges Q(a)+Q(b) rarely is neutral,
besides a certain value different to Zero; therefore its contribution is
considered and it has potential to be a huge surprise.
V-Two important characteristics of material:
These are not just 2 important characteristic of material,
they are 2 subjects that attracts a lot of researchers in history and now.
Although we can go along with the researchers but we can’t keep going ahead
without some brief about them.
1-Permeability:
The magnetic permeability of a material is the degree of magnetization that it
receives when it responds linearly to a magnetic field. The symbol denoted for
permeability is a Greek letter ‘’µ’’, which is measured in units of H/m (Henry
per meter) or N/A2 (Newton per Ampere squared). Empty space itself
has an electromagnetic permeability value, also known as the magnetic constant,
µ0=4π*10-7 N/A2
For the purpose of demonstrating a mathematical relationship
between µ and some magnetic field B that is influencing a medium of some king,
let’s assume that there is an auxiliary magnetic field H that represents the
way this B field influences the organization of magnetic dipoles in our medium.
According to the way we have set up situation, the relationship between the
fields B, H and our permeability µ is mathematically defined by the following
equation:
B=µH
In the above case, our permeability will be scalar as long as our
medium is isotropic. Isotropy refers to a certain organization of medium that
means it is uniform in all directions. A good example of the use of isotropy is
in the cosmological principle that is a part of the Big Bang Theory. It is
assumed, in the Big Bang model, that space is isotropic, meaning there are no
localized anomalies in space that would stop the universe from expanding in the
way we observe. Anisotropy is opposite of isotropy. We are able to use a scalar
for permeability if we are working with a second rank tensor for anisotropy
linear medium.
2-Susceptibility: Magnetic susceptibility is the degree of
magnetism of a material in response to an applied magnetic field. If the
magnetic susceptibility is positive, the material can be paramagnetic,
ferromagnetic or antiferromagnetic. In these cases the magnetic field is
strengthened by the presence of the material. Alternatively, if the magnetic
susceptibility is negative, the material is diamagnetic and as a result, the
magnetic field is weakened by the presence of the material.
If the ratio between the induced magnetization and the
inducing field is expressed in unit volume, volume susceptibility (k) is
defined as
K=M/H
Where M is the volume magnetization induced in a material of
susceptibility k by the applied external field H. Volume susceptibility is a
dimensionless quantity. The value depends on the measurement system used:
K(SI)=4π*k(cgs)=4π*G*Oe-1,
Where G and Oe are abrreviations for Gause and Orstedt
respectively. The SI system should be used.
Mass, or specific, susceptibility is defined as
X=k/r
Where r is the density of material. The dimensions of mass
susceptibility are therefore cubic meters per kilogram.
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