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ELECTROMAGNETISM
Magnets
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A magnet from Greek word (μαγνήτις λίθος magnḗtis 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
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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!
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The nickel iron core of the earth gives the
earth a magnetic field much like a bar
magnet.
History
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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, MICHAEL FARADAY showed that a changing
magnetic field can induce a current in a circuit.
In 1860, JAMES CLERK MAXWELL 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…
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In 1905, the theoretical implications of
electromagnetism led to Albert Einstein's theory of
special relativity.
Electromagnet
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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…
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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
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The word Electromagnetism is a compound form of
two Greek terms, ἢλεκτρον, ēlektron, "amber", and
μαγνήτης, magnētēs, "magnet".
It is a branch of physical science that deals with the
physical relations between electricity and
magnetism.
Introduction to Electromagnetic Fields
Fundamental laws of
classical electromagnetics
Special
cases
Electrostatics
Statics:
Input from
other
disciplines
Maxwell’s
equations
Magnetostatics

0
t
Electromagnetic
waves
Geometric
Optics
Transmission
Line
Theory
Circuit
Theory
Kirchoff’s
Laws
d  
Introduction to Electromagnetic Fields
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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.
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Classical Electromagnetism is a branch of
theoretical physics that studies consequences of the
electromagnetic forces between electric charges
and currents.
Introduction to Electromagnetic Fields
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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…
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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…
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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
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Fundamental vector field quantities in
electromagnetics:
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E 
Electric field intensity
units = volts per meter (V/m = kg m/A/s3)
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Electric flux density (electric displacement)
D 
units = coulombs per square meter (C/m2 = A s /m2)
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Magnetic field intensity
H 
units = amps per meter (A/m)
Magnetic flux density
B 
units = teslas = webers per square meter (T =
Wb/ m2 = kg/A/s3)
Introduction to Electromagnetic Fields
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Universal constants in electromagnetics:
 Velocity
of an electromagnetic wave (e.g., light)
in free space (perfect vacuum)
c  3 10 m/s
8
 Permeability
of free space
 0  4 10 7 H/m
 Permittivity
 Intrinsic
of free space:
 0  8.854 10 12 F/m
impedance of free space:
 0  120 
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Any Questions…????