Download magnetism

SUBMITTED TO:-
SUBMITTED BY:-
Mr. DINESH
KUMAR UPRAJ
REG. NO. :-5050070023
ROLL NO. :-60
INTRODUCTION
In physics, magnetism is one of the phenomena by which materials exert attractive
or repulsive forces on other materials. Some well-known materials that exhibit
easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and
their alloys; however, all materials are influenced to greater or lesser degree by the
presence of a magnetic field.
Magnetism also has other manifestations in physics, particularly as one of the two
components of electromagnetic waves such as light.
CONTENTS










History
Physics of magnetism
Magnets and magnetic materials
Magnetism, electricity, and special relativity
Magnetic fields and forces
Magnetic dipoles
Magnetic monopoles
Units of electromagnetism
SI units related to magnetism
Other units
History:Aristotle attributes the first of what could be called a scientific discussion on
magnetism to Thales, who lived from about 625 BC to about 545 BC. [1] In China,
the earliest literary reference to magnetism lies in a 4th century BC book called
Book of the Devil Valley Master (鬼谷子): "The lodestone makes iron come or it
attracts it."[1] The earliest mention of the attraction of a needle appears in a work
composed between 20 and 100 AD (Louen-heng): "A lodestone attracts a
needle."[2] The ancient Chinese scientist Shen Kuo (1031-1095) was the first
person to write of the magnetic needle compass and that it improved the accuracy
of navigation by employing the astronomical concept of true north (Dream Pool
Essays, 1088 AD), and by the 12th century the Chinese were known to use the
lodestone compass for navigation. Alexander Neckham, by 1187, was the first in
Europe to describe the compass and its use for navigation. In 1269 Peter
Peregrinus wrote the Epistola de Magnete, the first extant treatise describing the
properties of magnets.
An understanding of the relationship between electricity and magnetism began in
1819 with work by Hans Christian Oersted, a professor at the University of
Copenhagen, who discovered more or less by accident that an electric current
could influence a compass needle. This landmark experiment is known as Oersted's
Experiment. Several other experiments followed, with André-Marie Ampère, Carl
Friedrich Gauss, Michael Faraday, and others finding further links between
magnetism and electricity. James Clerk Maxwell synthesized and expanded these
insights into Maxwell's equations, unifying electricity, magnetism, and optics into
the field of electromagnetism. In 1905, Einstein used these laws in motivating his
theory of special relativity[3], requiring that the laws held true in all inertial
reference frames.
Electromagnetism has continued to develop into the twentieth century, being
incorporated into the more fundamental theories of gauge theory, quantum
electrodynamics, electroweak theory, and finally the standard model.
Physics of magnetism:Magnets and magnetic materials
Every electron, by its nature, is a small magnet (see Electron magnetic dipole
moment). Ordinarily, the countless electrons in a material are randomly oriented in
different directions, leaving no effect on average, but in a bar magnet the electrons
are aligned in the same direction, so they act cooperatively, creating a net magnetic
field.
In addition to the electron's intrinsic magnetic field, there is sometimes an
additional magnetic field that results from the electron's orbital motion about the
nucleus. This effect is analogous to how a current-carrying loop of wire generates a
magnetic field (see Magnetic dipole). Again, ordinarily, the motion of the electrons
is such that there is no average field from the material, but in certain conditions,
the motion can line up so as to produce a measurable total field.
The overall magnetic behavior of a material can vary widely, depending on the
structure of the material, and particularly on its electron configuration. Several
forms of magnetic behavior have been observed in different materials, including:





Diamagnetism
Paramagnetism
o Molecular magnet
Ferromagnetism
o Antiferromagnetism
o Ferrimagnetism
o Metamagnetism
Spin glass
Superparamagnetism
Magnetism, electricity, and special relativity
As a consequence of Einstein's theory of special relativity, electricity and
magnetism are understood to be fundamentally interlinked. Both magnetism
lacking electricity, and electricity without magnetism, are inconsistent with special
relativity, due to such effects as length contraction, time dilation, and the fact that
the magnetic force is velocity-dependent. However, when both electricity and
magnetism are taken into account, the resulting theory (electromagnetism) is fully
consistent with special relativity[4][5]. In particular, a phenomenon that appears
purely electric to one observer may be purely magnetic to another, or more
generally the relative contributions of electricity and magnetism are dependent on
the frame of reference. Thus, special relativity "mixes" electricity and magnetism
into a single, inseparable phenomenon called electromagnetism (analogously to
how special relativity "mixes" space and time into spacetime).
Magnetic fields and forces
The phenomenon of magnetism is "mediated" by the magnetic field -- i.e., an
electric current or magnetic dipole creates a magnetic field, and that field, in turn,
imparts magnetic forces on other particles that are in the fields.
To an excellent approximation (but ignoring some quantum effects---see quantum
electrodynamics), Maxwell's equations (which simplify to the Biot-Savart law in
the case of steady currents) describe the origin and behavior of the fields that
govern these forces. Therefore magnetism is seen whenever electrically charged
particles are in motion---for example, from movement of electrons in an electric
current, or in certain cases from the orbital motion of electrons around an atom's
nucleus. They also arise from "intrinsic" magnetic dipoles arising from quantum
effects, i.e. from quantum-mechanical spin.
The same situations which create magnetic fields (charge moving in a current or in
an atom, and intrinsic magnetic dipoles) are also the situations in which a magnetic
field has an effect, creating a force. Following is the formula for moving charge;
for the forces on an intrinsic dipole, see magnetic dipole.
When a charged particle moves through a magnetic field B, it feels a force F given
by the cross product:
where is the electric charge of the particle, is the velocity vector of the particle, and
is the magnetic field. Because this is a cross product, the force is perpendicular to
both the motion of the particle and the magnetic field. It follows that the magnetic
force does no work on the particle; it may change the direction of the particle's
movement, but it cannot cause it to speed up or slow down. The magnitude of the
force is where is the angle between the and vectors.
One tool for determining the direction of the velocity vector of a moving charge,
the magnetic field, and the force exerted is labeling the index finger "V", the
middle finger "B", and the thumb "F" with your right hand. When making a gunlike configuration (with the middle finger crossing under the index finger), the
fingers represent the velocity vector, magnetic field vector, and force vector,
respectively. See also right hand rule.
Lenz's law gives the direction of the induced electromotive force (emf) and current
resulting from electromagnetic induction. German physicist Heinrich Lenz
formulated it in 1834.
Magnetic dipoles
A very common source of magnetic field shown in nature is a dipole, with a "South
pole" and a "North pole"; terms dating back to the use of magnets as compasses,
interacting with the Earth's magnetic field to indicate North and South on the
globe. Since opposite ends of magnets are attracted, the north pole of a magnet is
attracted to the south pole of another magnet. Interestingly, this concept of
opposite polaraties attracting wasn't used in the naming convention for the earth's
magnetic field, so the earth's magnetic north pole (in Canada) attracts the magnetic
north pole of a compass see North Magnetic Pole.
A magnetic field contains energy, and physical systems stabilize into the
configuration with the lowest energy. Therefore, when placed in a magnetic field, a
magnetic dipole tends to align itself in opposed polarity to that field, thereby
canceling the net field strength as much as possible and lowering the energy stored
in that field to a minimum. For instance, two identical bar magnets placed side-toside normally line up North to South, resulting in a much smaller net magnetic
field, and resist any attempts to reorient them to point in the same direction. The
energy required to reorient them in that configuration is then stored in the resulting
magnetic field, which is double the strength of the field of each individual magnet.
(This is, of course, why a magnet used as a compass interacts with the Earth's
magnetic field to indicate North and South).
An alternative, equivalent formulation, which is often easier to apply but perhaps
offers less insight, is that a magnetic dipole in a magnetic field experiences a
torque and a force which can be expressed in terms of the field and the strength of
the dipole (i.e., its magnetic dipole moment). For these equations, see magnetic
dipole.
Magnetic monopoles:-
Since a bar magnet gets its ferromagnetism from electrons distributed evenly
throughout the bar, when a bar magnet is cut in half, each of the resulting pieces is
a smaller bar magnet. Even though a magnet is said to have a north pole and a
south pole, these two poles cannot be separated from each other. A monopole — if
such a thing exists — would be a new and fundamentally different kind of
magnetic object. It would act as an isolated north pole, not attached to a south pole,
or vice versa. Monopoles would carry "magnetic charge" analogous to electric
charge. Despite systematic searches since 1931, as of 2006, they have never been
observed, and could very well not exist.[6]
Nevertheless, some theoretical physics models predict the existence of these
magnetic monopoles. Paul Dirac observed in 1931 that, because electricity and
magnetism show a certain symmetry, just as quantum theory predicts that
individual positive or negative electric charges can be observed without the
opposing charge, isolated South or North magnetic poles should be observable.
Using quantum theory Dirac showed that if magnetic monopoles exist, then one
could explain the quantization of electric charge---that is, why the observed
elementary particles carry charges that are multiples of the charge of the electron.
Certain grand unified theories predict the existence of monopoles which, unlike
elementary particles, are solitons (localized energy packets). The initial results of
using these models to estimate the number of monopoles created in the big bang
contradicted cosmological observations — the monopoles would have been so
plentiful and massive that they would have long since halted the expansion of the
universe. However, the idea of inflation (for which this problem served as a partial
motivation) was successful in solving this problem, creating models in which
monopoles existed but were rare enough to be consistent with current
observations.[7]
Units of electromagnetism:SI units related to magnetism
SI electromagnetism units
Symbol
Name of Quantity
Derived Units
Unit
ampere (SI base
A
unit)
Base Units
I
Electric current
A = W/V = C/s
q
Electric charge, Quantity of
coulomb
electricity
C
A·s
V
Potential difference or
Electromotive force
volt
V
J/C = kg·m2·s−3·A−1
R, Z, X
Resistance, Impedance,
Reactance
ohm
Ω
V/A = kg·m2·s−3·A−2
ρ
Resistivity
ohm metre
Ω·m kg·m3·s−3·A−2
P
Power, Electrical
watt
W
V·A = kg·m2·s−3
C
Capacitance
farad
F
C/V = kg−1·m−2·A2·s4
Elastance
reciprocal farad
F−1
V/C = kg·m2·A−2·s−4
ε
Permittivity
farad per metre
F/m
kg−1·m−3·A2·s4
χe
Electric susceptibility
(dimensionless)
-
-
G, Y, B
Conductance, Admittance,
siemens
Susceptance
σ
Conductivity
S
Ω−1 = kg−1·m−2·s3·A2
siemens per metre
S/m
kg−1·m−3·s3·A2
B
Magnetic field (Magnetic
flux density)
tesla
T
Wb/m2 = kg·s−2·A−1 =
N·A−1·m−1
Φm
Magnetic flux
weber
Wb
V·s = kg·m2·s−2·A−1
H
Magnetizing field
ampere per metre
A/m
Reluctance
ampere-turn per
A/Wb kg−1·m−2·s2·A2
weber
L
Inductance
henry
μ
Permeability
henry per metre
H/m
χm
Magnetic susceptibility
(dimensionless)
H
A·m−1
Wb/A = V·s/A =
kg·m2·s−2·A−2
kg·m·s−2·A−2
Other units


gauss-The gauss, abbreviated as G, is the cgs unit of magnetic flux
density or magnetic induction (B).
oersted-The oersted is the CGS unit of magnetic field strength.


maxwell-is the CGS unit for the magnetic flux.
μo -common symbol for the permeability of free space (4πx10-7
N/(ampere-turn)²).
REFERENCES
WEB SITE:-
www.winkipedia.com
www.answer.com
www.informatics.com
REFRENCE BOOK:1. Electricity and Magnetism , DR.A.K SIKRI
2. Fundamental of Physics , D.Halliday , R.Resnik , J.Walker