Understanding
Electromagnetic Induction and
Electromagnetism
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Faculty: B. Allen
Electromagnetism
Relates to the magnetic field generated around a conductor
when current is passing through it.
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Coil
Coil – A number of turns of wire wound around a
core to produce magnetic flux (an electromagnet) or
to react to a changing magnetic flux (an inductor).
Electromagnet – A magnet consisting of a coil
wound on a soft iron or steel core. When current is
passed through the coil, a magnetic field is generated
and the core is strongly magnetized to concentrate
the magnet field.
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Faculty: B. Allen
Left-hand rule
If the fingers of the left hand are placed around the wire so
that the thumb points in the direction of the electronic current
flow, the fingers
will be pointing
in the direction
of the magnetic
field being
produced by the
conductor.
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Faculty: B. Allen
Magnet Terms
Maxwell – One magnetic line of force or flux is
called a Maxwell.
Magnet Flux (φ) – The magnetic lines of force
produced by a magnet.
Weber – 108 Maxwells.
Flux Density (β) – A measure of the strength of a
wave.
Flux Density (β) = Magnet Flux(φ)/Area (A)
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Magnet terms (continued)
Magnetomotive Force (mmf) – A force that
produces a magnetic field.
mmf = I(current) × N(turns)
= I × N (ampere-turns)
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Magnetizing force (H)
Magnetizing Force – Also called magnetic
field strength, it is the magnetomotive force
per unit length at any given point in a
magnetic circuit.
I × N mmf
H=
=
l
l
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Reluctance (R)
Reluctance – Resistance to the flow of magnetic lines
of force.
Magnetic
Reluctance (R) = mmf/φ
Measured in Ampere-Turns/Weber
Electric
Resistance (R) =V/I
Measured in Ohms
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Permeability (µ)
The measure of how much better a material
is as a path for magnetic lines of force with
respect to air, which has a permeability of 1.
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Magnetic
Permeability (µ) = 1/(R) reluctance
Electric
Conductance (G) = 1/ (R) resistance
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Permeabilities of various
materials
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Flux density (Β) vs. magnetizing
force (H)
Β-Η curve – A curve plotted on a graph to show successive
states during magnetization of a ferromagnetic material.
Saturation Point – The point beyond which an increase in
one of the quantities produces no increase in the other.
Hysteresis – A lag between cause and effect. With
magnetism, it is the amount that the magnetization of a
material lags the magnetization force due to molecular
friction.
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Remanence or Retentivity – The amount of a
material that remains magnetized after the
magnetizing force has been removed.
Coercive Force – Magnetizing force needed to
reduce the residual magnetism within a material to
zero.
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Applications of
electromagnetism
Magnetic type circuit breaker
Electric bell
Relay
Solenoid-type electromagnet
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Relay
Relay – An
electromechanical
device that opens or
closes contacts when
a current is passed
through a coil.
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Solenoid
Solenoid – A coil and movable iron core that, when energized
by an alternating or direct current, will pull the core into a
central position.
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Electromagnetic induction
Electromagnetic Induction – The voltage produced in
a coil due to relative motion between the coil and
magnetic lines of force.
Faraday’s Law – When a magnetic field cuts a
conductor, or when a conductor cuts a magnetic field,
an electric current will flow in the conductor if a
closed path is provided over which the current can
circulate.
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Electromagnetic induction
(continued)
Lenz’s Law – The current induced in a circuit due to
a change in the magnetic field is so directed as to
oppose the change in flux, or to exert a mechanical
force opposing the motion.
Weber – A unit of magnetic flux. One weber (108
maxwells) is the amount of flux that, when linked
with a single turn of wire for an interval of one
second, will induce an electromotive force of one
volt.
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Generator
Generator – A device used to convert a mechanical
energy
input into
an electrical
energy
output.
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Parts of a generator
Armature – The rotating or moving components of a
magnetic circuit
Stator – The stationary components of a magnetic
circuit
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Generator operation
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Moving coil microphone
Microphone – Electroacoustic transducer
that responds and converts a sound wave
input into an equivalent electrical wave
output.
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End of
Electromagnetic Induction and
Electromagnetism
Online Resource for ETCH 213
Faculty: B. Allen