Download Electromagnetism Lecture 1

Electromagnetism
Lecture 1
Course Outline as a Reminder
Module Leader: Engineer Bilal Ahmad
MSC in Mobile and Distributed Computing
Networks (Leeds Met University)
BS in Telecom Engineering (FAST, Pakistan)
(Registered from Pakistan Engineering Council)
In this course Assignments marks are 10%, Quizzes
all surprised 10%, Class Participation 10%, Mid
Term Examination 30% and Final Examination
40%.
Good Luck  I believe all of you are capable to get
Grade A+. www.csanditllu.wordpress.com
Electricity
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If one defines electricity, it is a phenomenon that
involves electric charges.
Common examples are static electricity and
lightening.
For lightening see next slide.
For static electricity there are two ways to
observe, one is voltmeter and other is if you want
to personally experience, feel free to do that at
your own risk.
Lightening
Explanation
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The existence of electricity, the phenomenon
associated with stationary or moving electric
charges, has been known since the Greeks
Discovered that amber rubbed with fur, attracted
light objects such as feathers.
Explanation (Continued)
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Ben Franklin proved the electric nature of
lightning (The Famous Key Experiment) and also
established the conventional use of negative and
positive types of charges.
Lightning Rod Experiment
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In 1752, Franklin proposed an experiment with
conductive rods to attract lightning to a Leyden
Jar. (An Early form of capacitor)
In Physics and Electrical Engineering, a conductor
is an object or type of material which permits the
flow of electric charges in one or more direction.
For example a wire is a semi conductor that can
carry electricity along its length.
A capacitor is a passive two terminal electrical
component used to store energy electro-statically
in an electric field.
Kite Experiment
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Franklin Realized the dangers of using conductive
rods.
Instead he used a kite.
The increased height allowed him to stay on the
ground and the kite was less likely to electrocute
him.
According to the Legend, Franklin kept the string
on the kite dry at his end while the string was
allowed to get wet in the rain to provide
conductivity.
A key was attached to the string and connected to
a Leyden jar.
Leyden Jar
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A Leyden Jar is a device that stores electricity
between two electrodes on the inside and outside
of a glass jar.
It was originally a form of a capacitor. It consisted
of a Glass Vial, partially filled
with sheets of metal foil.The
top of which was closed by a
cork pierced with wire/ nail.
Kite Experiment (Continued)
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Franklyn assumed that the jar will would
accumulate electricity from the lighting.
The kite wasn’t struck from the visible light
otherwise his nephew would have passed away.
What Franklin noticed was that the strings of the
kite were repelling each other and deducted that
the Leyden jar was charged.
Franklin reportedly received a mild shock by
moving his hands near the key afterwards, because
he had estimated, lightning has negatively charged
the key and the Leyden jar. Proving the electric
nature of the charge.
Controversy
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In one of the Television shows ‘Myth-Busters’ the
host has tried to emulate a variation on the
famous experiment.
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"You can get electricity down a [wet] kite string."
Electricity will NOT travel down a dry kite string.
The key will conduct a static charge, even when
NOT struck by lightning.
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Discussion (Continued)
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It was also known that certain materials blocked
electric charge.
They are called insulators, such as glass or wood.
Other materials that transferred electric charge
with ease, called conductors. Such as metal.
By the 18th century, physicist Charles Coulomb
defined the quantity of electricity later known as
coulomb and determined the force law between
electric charges.
It was known as coulomb law.
Discussion (Continued)
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Coulomb law is that the electrical forces are
inversely proportional to the distance of the
charges squared, and proportional to the product
of charges.
By the end of 18th Century, we had determined
that electric charge could be stored in a
conducting body if it is insulated from its
surroundings.
The first device was a Leyden Jar.
Discussion (Continued)
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Coulomb found that the force F between one
charge q1 and a second charge q2 is equal to the
product of the charges divided by the square of
the distance r between them, or F = q1 q2 /r
The force can be either attractive or repulsive,
because the source of the force, electric charge,
exists in two varieties, positive and negative.
The force between opposite charges is attractive,
whereas bodies with the same kind of charge
experience a repulsive force
Modern Atomic Theory
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Modern Atomic Theory explains this as the ability
of atoms to either lose or gain an outer electron.
Thus exhibit a net positive charge or gain a net
negative charge.
Today we know that the basic quantity of electric
charge is the electron and one coulomb is about
6.24 x 10 P 18 Electrons.
The battery was invented in 19th Century.
Electric Fields
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The mathematical problem of describing the
motion of electric charges leads to the
development of the field concept.
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The use of fields (as in electric field, gravitational
field, force field) is mathematical tool to describe
physical events.
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The field itself is not observable but its effect is
visible.
To Map a Field
Electric Fields (Continued)
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The shape and resulting strength, of an electric
field is dependent on the number and the position
of the electric charges.
Each point is space can be assigned a vector to
determine the magnitude and direction of the
motion.
See
the
next
slide
for
diagrammatic
representation.
Magnetism
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Related to electricity, is the phenomenon of
magnetism
Magnetism results from the motion of electric
charges, although historically we know of the
behavior of magnetic fields from bar magnets
magnetic fields deflect moving charges or other
magnets
Magnets have north and south poles, similar to
positive and negative charge, but poles can never
be separated
Magnetism (Continued)
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The simplest magnetic field results from an
electric current circulating in a loop bar, or
permanent, magnets result from small atomic
dipole loops which sum to produce a macroscopic
magnetic field
Difference between current and voltage
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Current is the rate at which electric charge flows
past a point in a circuit.
In other words current is the rate of flow of
electric charge.
Voltage is the electrical force that would drive an
electric current between two points.
In other words voltage is energy per unit charge.
The Symbol of current is I and Symbol for voltage
is V
The unit of current is amps or amperage and for
voltage is volts or voltage.
Difference between current and voltage
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The measuring instrument for current is
Ammeter and for voltage is voltmeter.
Current create magnetic field and voltage create
an electrostatic field.
Current is the same through all the components
connected in series and distributed if the
components are connected in parallel and for
voltage is the other way around as compared to
the current.