Theory of EMF(24EL Sec
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1 & 2)
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JAMSHORO
Department
of
Electrical
Engineering
Dr. Abdul Hakeem Memon
Associate Professor
Electrical Engineering,
MUET, Jamshoro
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Department
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Theory of EMF
Introduction to “Theory of
EMF”
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◼ This subject deals with Electromagnetic Fields
which is a combination of invisible electric and
magnetic fields of force. They are generated by
natural phenomena like the Earth’s magnetic
field but also by human activities, mainly using
electricity.
◼ Cell phones, power lines and computer screens
are examples of equipment that generates
electromagnetic fields.
◼ Most man-made electromagnetic fields reverse
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their direction at regular intervals of time,
ranging from high radio frequencies (mobile
phones) through intermediate frequencies
(computer screens) to extremely low
frequencies (power lines).
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◼ Figure describes the Spectrum of Frequency in
Hz and Sources of those electromagnetic fields
Importance of Theory of EMF
◼ Theory of EMF is the study of the underlying
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laws that govern the manipulation of electricity
and magnetism, and how we use these laws to
our advantage.
◼ Theory of EMF is the source of fundamental
principles behind many branches of electrical
engineering and indirectly impacts many other
branches.
◼ EM fields and forces are the basis of modern
electrical systems. It represents an essential and
fundamental background that underlies future
advances in modern communications, computer
systems, signal processing, and energy systems,
power system protection.
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Applications of Theory of EMF
M in the field of engineering applications. In
U addition, this caused a great impact on various
fields such as medical, industrial, space,
E protection systems etc.
T ◼ We can find enormous practical application of
◼ Electromagnetism has created a great revolution
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electromagnetism in everyday life from domestic
appliances to research applications.
◼ In
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domestic applications we can observe the
phenomena of EMF in lighting, heating and
kitchen appliance.
◼ In communication systems this exist in all
telecommunication equipment and
communication networks,
◼ In industrial systems this can be applied in
motors, generators, sensor and actuator devices,
etc.
◼ Some of the application areas of
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electromagnetism are enlisted below:
◼ Household appliances E.g. Fans, fluorescent
lights, security systems, etc.
◼ Industrial
applications
E.g.
Industrial
machinery, relays, sensors, etc.
◼ Magnetic Levitation Trains E.g. Electric Trains
◼ Communication System E.g. Radar signals,
Radio and TV signals etc.
◼ Medical System E.g. MRIs, Scanners, X-rays
etc
Applications of EMF
◼ Electromagnetic
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principles find application in
various disciplines such as microwaves, x-rays,
antennas, electric machines, plasmas, etc.
◼ Electromagnetic fields can be used to produce
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heat such as devices like induction heaters for
melting, forging, annealing, surface hardening.
◼ Electromagnetic devices include transformers,
radio, television, mobile phones, radars, lasers,
etc.
◼ A hard drive reads and
writes data by using
electromagnetism.
M
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E ◼ Trans rapid Train: It is a ◼ Hard drive:
German-developed high-speed Magnetic Data
T monorail train using magnetic Storage
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levitation.
Typical sources of electromagnetic fields
Frequency range
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Static
ELF [Extremely Low Frequencies]
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IF [Intermediate Frequencies]
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RF
[Radio Frequencies]
Engineering
Frequencies
Some examples of exposure sources
0 Hz
video display units; MRI (medical imaging)
and other diagnostic or scientific
instrumentation; industrial electrolysis;
welding devices
0-300 Hz
power lines; domestic distribution lines;
domestic appliances; electric engines in cars,
trains and tramways; welding devices
300 Hz - 100 kHz
video display units; anti-theft devices in
shops; hands-free access control systems,
card readers and metal detectors; welding
devices
mobile telephones; broadcasting and TV;
100 kHz - 300 GHz microwave ovens; radar and radio
transceivers; portable radios
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◼ Electric and magnetic field exist nearly
everywhere.
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ELECTROMAGNETIC FIELD
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Static Field
◼ A
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static field refers to any field (electric,
magnetic, gravitational, etc.) that does not
change with time.
◼ It’s a general term
◼ For example:
◼ A static electric field is created by stationary
electric charges.
◼ A static magnetic field is produced by steady
(non-varying) electric currents or permanent
magnets.
◼ In essence, "static" just means "unchanging with
time".
Static Electric Field
◼ Definition:
M ◼ Equation:
U ◼ The electric field E from a point charge 𝑞 at a
distance 𝑟 is:
E
T ◼ Where:
◼ Created by stationary electric charges.
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◼ ε0 is the vacuum permittivity
◼ r^
is the unit vector pointing from the charge to
the observation point
◼ Example::
◼ A
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positively charged metal sphere creates a
radial static electric field around it.
◼ Visual::
◼ Imagine lines radiating outward from a positive
charge:
Static Magnetic Field
◼ Definition:
M magnets. It does not change with time.
U ◼ Equation:
◼ For a long straight wire carrying a steady current
E 𝐼, the magnetic field B at a distance 𝑟 is given by
T Ampère's Law
◼ Produced by steady (DC) currents or permanent
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Where:
◼ The direction of 𝐵⃗ is tangent to circles around
the wire (use the right-hand rule).
◼ Example::
◼ The magnetic field
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around a current-carrying
wire (DC).
◼ The field from a bar magnet.
◼ Visual 1:
◼ Current-Carrying Wire (Top View)
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◼ (Use your right-hand rule: Thumb in direction
of current, fingers curl in direction of field)
◼ Visual 2: Bar Magnet
◼ Current-Carrying Wire (Top View)
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◼ (Use your right-hand rule: Thumb in direction
of current, fingers curl in direction of field)
Key Comparison
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