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Nov 16, 2013 (3 years and 6 months ago)

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ELECTROMAGNETISM

Magnets


A magnet from Greek word (
μαγνήτις

λίθος

magn

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








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0
Any Questions…????