ELECTROMAGNETISM
Magnets
A magnet from Greek word (
μαγνήτις
λίθος
magn
ḗ
tis
líthos
,
"
Magnesian
stone").
Magnets have been known for centuries.
The Chinese and Greeks knew about the “magical” properties
of magnets.
The ancient Greeks used a stone substance called “magnetite.”
They discovered that the stone always pointed in the same
direction. Later, stones of magnetite called “lodestones” were
used in navigation.
An object that is surrounded by a magnetic field and that has
the property, either natural or induced, of attracting iron or
steel.
William Gilbert, an
English physician, first
proposed in 1600 that the
earth itself is a magnet,
and he predicted that the
Earth would be found to
have magnetic poles.
What is Magnetism
Magnetism
is the properties and interactions of
magnets.
The earliest magnets were found naturally in the mineral
magnetite
which is abundant the rock

type
lodestone
. These
magnets were used by the ancient peoples as compasses to
guide sailing vessels.
Magnets produce magnetic forces and have magnetic field
lines.
Magnets
have two ends or poles, called north and south
poles. At the poles of a magnet, the magnetic field lines
are closer together.
Unlike poles of magnets attract each other and like
poles of magnets repel.
The Earth is like a giant magnet!
The nickel iron core of the earth gives the
earth a magnetic field much like a bar
magnet.
History
In
1820
,
Hans
Christian
Oersted
discovered
the
connection
between
electricity
and
magnetism
when
he
observed
the
magnetic
needle
of
a
compass
was
deflected
by
an
electric
current
in
a
nearby
wire
.
In
1831
,
M
ICHAEL
F
ARADAY
showed
that
a
changing
magnetic
field
can
induce
a
current
in
a
circuit
.
In
1860
,
J
AMES
C
LERK
M
AXWELL
predicted
that
a
changing
electric
field
has
an
associated
magnetic
field
and
wrote
the
mathematical
equations
that
describe
the
force
of
electromagnetism
for
the
first
time
.
Cont…
In 1905, the theoretical implications of
electromagnetism led to Albert Einstein's theory of
special relativity.
Electromagnet
When an electric current is passed through a
coil of wire wrapped around a metal core, a
very strong magnetic field is produced. This is
called an
electromagnet.
Cont…
We can make an electromagnet stronger by
doing these things:
wrapping the coil around an iron core
adding more turns to the coil
increasing the current flowing through the coil.
Electromagnetism: Definition
The word
Electromagnetism
is a compound form of
two
Greek
terms,
ἢλεκτρον
,
ē
lektron
, "
amber
", and
μαγνήτης
,
magn
ē
t
ē
s
, "
magnet
".
It is a branch of physical science that deals with the
physical relations between electricity and
magnetism.
Introduction to Electromagnetic Fields
Maxwell’s
equations
Fundamental laws of
classical electromagnetics
Special
cases
Electro

statics
Magneto

statics
Electro

magnetic
waves
Kirchoff’s
Laws
Statics:
0
t
d
Geometric
Optics
Transmission
Line
Theory
Circuit
Theory
Input from
other
disciplines
Introduction to Electromagnetic Fields
Maxwell’s Equation
Maxwell's
equations
are
a
set
of
partial
differential
equations
that,
together
with
the
Lorentz
force
law,
form
the
foundation
of
classical
electrodynamics
(classical
electromagnetism),
classical
optics,
and
electric
circuits
.
Maxwell's
equations
describe
how
electric
and
magnetic
fields
are
generated
and
altered
by
each
other
and
by
charges
and
currents
.
Classical
Electromagnetism
is
a
branch
of
theoretical
physics
that
studies
consequences
of
the
electromagnetic
forces
between
electric
charges
and
currents
.
Introduction to Electromagnetic Fields
Electromagnetics
is the study of the effect of
charges at rest and charges in motion.
Some special cases of electromagnetics:
Electrostatics
: charges at rest (Static Electricity)
Magnetostatics
: charges in steady motion
Electromagnetic waves
: waves excited by charges in
time

varying motion.
Introduction to Electromagnetic Fields
•
transmitter and receiver
are connected by a “field.”
Cont…
When an event in one place has an effect on
something at a different location, we talk about the
events as being connected by a “field”.
A
field
is a spatial distribution of a quantity; in
general, it can be either
scalar
or
vector
in nature.
Cont…
Electric and magnetic fields:
Are vector fields with three spatial components.
Vary as a function of position in 3D space as well as
time.
Are governed by partial differential equations derived
from Maxwell’s equations.
Introduction to Electromagnetic Fields
Fundamental vector field quantities in
electromagnetics
:
Electric field intensity
Electric flux density (electric displacement)
Magnetic field intensity
Magnetic flux density
units = volts per meter (V/m = kg m/A/s
3
)
units = coulombs per square meter (C/m
2
= A s /m
2
)
units = amps per meter (A/m)
units =
teslas
=
webers
per square meter (T =
Wb
/ m
2
= kg/A/s
3
)
E
D
H
B
19
Introduction to Electromagnetic Fields
Universal constants in electromagnetics:
Velocity of an electromagnetic wave (e.g., light)
in free space (perfect vacuum)
Permeability of free space
Permittivity of free space:
Intrinsic impedance of free space:
m/s
10
3
8
c
H/m
10
4
7
0
F/m
10
854
.
8
12
0
120
0
Any Questions…????
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