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Unit 6, Assignment 4 - Magnetism, Transformers, Motor & Generators (P7, P8, P9 & D2)
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- PEARSON (PEARSON)
BTEC Engineering Level 3
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Unit 6 Magnetism, Transformers & Motors/Generators Assignment 4Firstly, a magnetic field is an object that is strong enough to
affect other materials; the molecules within the magnet are lined
up to face one direction, which gives the magnet its field.
Temporary magnets’ molecules align up for a set period of time
before it loses its magnetism; additionally, some molecules can
line up permanently, making a permanent magnet. Some of the
properties of a magnetic field are that magnets attract to each
other as long as they are opposites (north pole & south pole), & like poles repel. Magnetic
objects that contain iron, cobalt, cobalt & nickel; the force of the magnet at the poles are far
greater than the middle of the magnet. Also, if a magnet is hanging by a thread & is able to
move freely, the south pole of the magnet will move towards the north pole of the earth &
vice versa.
The diagrams on the right show a magnetic field with arrows
on top of lines (magnetic field lines); these arrows represent the
direction of the magnetic field. Likewise, at any point where
two magnetic fields are acting & a compass needle doesn’t
point in any specific path, then there is no subsequent field at
the point; and this is known as the neutral or null point; & this
is shown as an ‘x’ on the second diagram. An interesting fact
about magnets is that if a bar magnet was to be cut in half, (the
north-pole is no longer attached to the south-pole) each piece
would have its on north & south-pole no matter what.
A magnetic field can be compared to the lines of a magnetic flux, which is essentially the
amount of magnetic field in an object. Furthermore, a magnetic flux flows from one pole to
the other. The flux takes the path with the least resistance between the poles, which is why
they form close loops from pole to pole.
The term ferromagnetic is relating to a substance like iron, that below a certain temperature,
the Curie point (temperature at which certain materials start losing their permanent magnetic
properties so that they can be substituted by induced magnetism) can retain magnetization in
the absence of an outer magnetic field. A few ferromagnetic materials that are strongly
attracted by a magnetic force are Iron, Nickel, Gadolinium & many more. Additionally,
nearly every electronic item equipment produced in this day of age contains a few
ferromagnetic material; some of these products are loudspeakers, motors, transformers &
many more.
Lastly I will be explaining the process of electromagnetic shielding, which is the run through
of surrounding electronics & cables with magnetic materials to protect against arriving or
departing emissions of electromagnetic frequencies (EMF). EM Shielding is conducted for
many reasons; one of the main purposes of EM Shielding is to stop electromagnetic
interference (EMI) from affecting delicate electronics. Metallic mesh for example protects
one component from affecting another inside a specific device, such as a mobile phone to
shield the electronics from its cellular transmitter. There a variety of different materials &
techniques used for EM Shielding, such as wires, this can be covered by a metallic foil to
block roaming EMI from the cased wires. Magnetic materials has to be used for EM
Shielding in places where the magnetic fields slowly change below the 100khz range since a
Faraday cage solution is unsuccessful in these types of situations.
Moving onwards to the relationship between flux density (B) & field strength, we first
must know what these are. Starting with field strength, which can express one way of the
intensity of a magnetic field; a difference can be certain between the field strength (H), which
is measured in amperes (A) per meter (A/m), & flux density (B), which is measured in
newton meters per ampere (Nm/A).
P7, P8, P9, D2 Fahim Mohammed
, Unit 6 Magnetism, Transformers & Motors/Generators Assignment 4
The magnetic field can be seen as magnetic field lines; so the field
strength links to the density of the field lines; so, the total number of
magnetic field lines piercing an area is called the magnetic flux. This
is measured in tesla meter squared (T · m2, also known as the weber
(Wb)). Furthermore, magnetic flux density diminishes with rising
distance from a straight current that carries wire or a straight line
connecting a pair of magnetic poles around; moreover, at any given location in the area of a
current carrying wire, the flux density is directly comparative to the current in amperes. The
flux Φ
equation for magnetic flux density (B) =
area( A)through which flux passes
Φ
B=
A
Φ=BxA
Consequently, the magnetic field strength (H) has the geometry of a differential 1 – form, is
united over a path & is defined in terms of time varying charge distributions (current).
However, the magnetic flux density (B) has the geometry of a differential 2 – form, joined
over surfaces & is defined in terms of the Lorentz force (force that is released by a magnetic
field on a moving electric charge). So, the relationships between these two are that they are
physically related through the institute calculations, which depends on the details of the
circumstance.
On to the last part of this section, which is electromagnetic induction; this is essentially the
process where a conductor that is placed in a charging magnetic field causes the production of
the voltage across the conductor; this process causes an electrical current.
The principles of electromagnetic induction are all applied in a variety of devices & systems,
such as, current clamp, induction motors, transformers, electrical generators & more. With an
electrical generator as an example, when a permanent magnet is moved to a conductor, an
electromotive force (EMF) is created; if a wire is joined through an electrical load, the current
will flow & electrical energy will be made, which’ll convert the mechanical energy to
electrical.
In the year 1831, Michael Faraday was known as a physicist who gave one of the basic laws
of electromagnetic induction, which is known as Faraday’s law of Electromagnetic Induction.
This law clearly explains the principle of electrical motors, transformers, inductors &
generators; it also shows the relationship between an electric circuit & a magnetic field.
Faraday performed an experiment where he found out how EMF is prompted in a coil when
flux connected with it changes; the conclusion of this experiment was that whenever there is
comparative motion between a conductor & a magnetic field, the flux’s bond with a coil alters
& this change in flux brings a voltage across a coil.
Michael Faraday created two laws based on the experiments he
organised. The first law (Faraday’s First Law) explains that “Any
change in the magnetic field of a coil of wire will cause an EMF to
be induced in the coil. This EMF induced is titled as an induced
EMF & if the conductor circuit is shut, the current will also flow
through the circuit & this current is called an induced current.”
There are a few ways of which a magnetic field can be altered;
some of the ways are by changing the area of a coil placed in a magnetic field, by moving a
magnet near or from afar the coils & spinning the coil comparative to the magnet. The second
law (Faraday’s Second Law) stated “that the magnitude of EMF induced in the coil is equal
to the rate of change of flux that connects with the coil; the flux linkage of the coil is the
product of number of turns in the coil & flux associated with the coil.” An example
P7, P8, P9, D2 Fahim Mohammed
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