What are electromagnets and what are their application.

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Electric current flowing through a wire wound around an iron nail creates a magnetic field, which caused an iron
nail to become a temporary magnet. The nail can then be used to pick up paper clips. When the electric current is cut off, the nail loses its magnetic property and the paper clips fall off.
1. International Journal of Industrial Electronics and Electrical Engineering, ISSN(p): 2347-6982, ISSN(e): 2349-204X
Volume-5, Issue-8, Aug.-2017, http://iraj.in
Bachelor of Electrical Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran
E-mail: [email protected]
Abstract- Electric current flowing through a wire wound around an iron nail creates a magnetic field, which caused an iron
nail to become a temporary magnet. The nail can then be used to pick up paper clips. When the electric current is cut off, the
nail loses its magnetic property and the paper clips fall off. The students will make an elecromagnet that will attract a paper
clip. They will then increase the strength of an electromagnet(improve on their initial design) so that it will attract an
increased number of paper clips. The participants will also compare the properties of magnets and electromagnets. However,
unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the
magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors. Electromagnets
are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel. We will investigate
engineering and industrial applications of the case study.
Keywords- Electromagnet, Application, Engineering.
I. INTRODUCTION William Sturgeon. If you have ever played with a
really powerful magnet, you have probably noticed
Electromagnet, device in which magnetism is one problem. You have to be pretty strong to separate
produced by an electric current. Any electric current the magnets again! Today, we have many uses for
produces a magnetic field, but the field near an powerful magnets, but they wouldn’t be any good to
ordinary straight conductor is rarely strong enough to us if we were not able to make them release the
be of practical use. A strong field can be produced if objects that they attract.
an insulated wire is wrapped around a soft iron core
and a current passed through the wire. The strength of In 1820, a Danish physicist, Hans Christian Oersted,
the magnetic field produced by such an electromagnet discovered that there was a relationship between
depends on the number of coils of wire, the electricity and magnetism. Thanks to Oersted and a
magnitude of the current, and the magnetic few others, by using electricity, we can now make
permeability of the core material; a strong field can huge magnets. We can also cause them to release
be produced from a small current if a large number of their objects.
turns of wire are used. Unlike the materials from
which permanent magnets are made, the soft iron in II. BAR MAGNET
the core of an electromagnet retains little of the
magnetism induced in it by the current after the The lines of magnetic field from a bar magnet form
current has been turned off. closed lines. By convention, the field direction is
This property makes it more useful than a permanent taken to be outward from the North pole and in to the
magnet in many applications. Electromagnets are South pole of the magnet. Permanent magnets can be
used to lift large masses of magnetic materials, such made from ferromagnetic materials.
as scrap iron. They are essential to the design of the As can be visualized with the magnetic field lines, the
electric generator and electric motor and are also magnetic field is strongest inside the magnetic
employed in doorbells, circuit breakers, television material. The strongest external magnetic fields are
receivers, loudspeakers, atomic particle accelerators, near the poles. A magnetic north pole will attract the
and electromagnetic brakes and clutches. south pole of another magnet, and repel a north pole.
Electromagnetic propulsion systems can provide The magnetic field lines of a bar magnet can be
motive power for spacecraft. Electromagnets are also traced out with the use of a compass. The needle of a
essential to magnetic levitation systems. compass is itself a permanent magnet and the north
indicator of the compass is a magnetic north pole.
Such systems often use a special kind of The north pole of a magnet will tend to line up with
electromagnet whose coil is made of a the magnetic field, so a suspended compas needle
superconducting metal. Because the coils of a will rotate until it lines up with the magnetic field.
superconducting electromagnet offers no resistance to Unlike magnetic poles attract, so the north indicator
the flow of electricity, no energy is wasted by the of the compass will point toward the south pole of a
development of heat, and the magnetic field produced magnet. In response to the Earth's magnetic field, the
by the magnet can be very strong. Superconducting compass will point toward the geographic North Pole
magnets are used in magnetic-resonance imaging, and of the Earth because it is in fact a magnetic south
can also be used for energy storage. The first practical pole. The magnetic field lines of the Earth enter the
electromagnet was invented early in the 19th cent. by Earth near the geographic North Pole.
Electromagnets and their Applications
2. International Journal of Industrial Electronics and Electrical Engineering, ISSN(p): 2347-6982, ISSN(e): 2349-204X
Volume-5, Issue-8, Aug.-2017, http://iraj.in
A transformer is simply two electromagnets which
are magnetically coupled together. There is electrical
isolation between the two windings, but power can be
transferred from one winding (the primary) to the
other winding (the secondary) via the alternating
magnetic field. They work on AC voltages. The ratio
of the secondary output voltage to the primary input
voltage is equal to the ratio of the number of turns in
the secondary winding to the number of turns in the
primary winding. (i.e., Vout/Vin =
The photo on the left is a control transformer, and
takes 230Vac in and drops it to 115Vac out for
control circuits in industry. You can also turn it
around and put 115Vac in and get 230Vac out.
III. ELECTROMAGNET Transformers have a kVA rating which is the rated
output Voltage times the rated output Amps divided
Electromagnets are usually in the form of iron core by 1000. The one above is rated at 0.200kVA or
solenoids. The ferromagnetic property of the iron 200VA. The two photos on the right show how to
core causes the internal magnetic domains of the iron demonstrate the transformer action using two coils
to line up with the smaller driving magnetic field and the AC electromagnet from our electromagnet
produced by the current in the solenoid. The effect is experiments.
the multiplication of the magnetic field by factors of This transformer was called a Sparker or Ignition
tens to even thousands. coil, used to create the spark needed for the spark-
plugs in cars from the '30s. It has a few turns for a
primary winding, and lots of turns for a secondary
winding. The mechanism at the end would open and
close the circuit several times a second creating an
AC like voltage on the primary (Since it was operated
from a 12V battery, and transformers don't work on
DC, a method was needed to create an AC type of
voltage on the primary coil). The secondary has
thousands of turns on it, creating a high voltage of
around 30,000V which will arc about 10mm through
the air.
Unlike a copper wire, the current density of a current
carrying disc is not uniform across its cross-sectional
IV. ELECTROMAGNETISM area, but is instead a function of the ratio of the inner
diameter of the disc to an arbitrary radius within the
Electromagnetism is produced when an electrical disc. The implications of this relationship is that the
current flows through a simple conductor such as a current density decreases with an increase in radius.
length of wire or cable, and as current passes along As such, the bulk of the current is flowing closer to
the whole of the conductor then a magnetic field is the inner radius of the disc. Large discs (i.e. disc with
created along the whole of the conductor. The small a large difference between their inner and outer
magnetic field created around the conductor has a radius) will have a larger discrepancy in the current
definite direction with both the “North” and “South” density between the inner and outer portions of the
poles produced being determined by the direction of disc. This will reduce the efficiency and cause
the electrical current flowing through the conductor. additional complications in the system because there
Therefore, it is necessary to establish a relationship will be a more substantial temperature and stress
between current flowing through the conductor and gradient along the disc. As such, a series of nested
the resultant magnetic field produced around it by this coils is often used as it will more evenly distribute the
flow of current allowing us to define the relationship current across a large combined area as opposed to a
that exists between Electricity and Magnetism in the single coil with large discs. The non-uniform current
form of Electromagnetism. density must also be considered when calculating the
Electromagnets and their Applications
3. International Journal of Industrial Electronics and Electrical Engineering, ISSN(p): 2347-6982, ISSN(e): 2349-204X
Volume-5, Issue-8, Aug.-2017, http://iraj.in
magnetic flux density. Ampere's Law for a basic magnetic field through a coil of wire can be found
current carrying loop of wire gives that the on-axis from a form of the right-hand rule. If the fingers of
magnetic flux is proportional to the current running the right hand are curled around the coil in the
through the wire and is related to the basic geometry direction of current flow (conventional current, flow
of the loop, but is not concerned with the geometry of of positive charge) through the windings, the thumb
the cross section of the wire. The current density is points in the direction of the field inside the coil. The
uniform across the cross-sectional area of a wire. This side of the magnet that the field lines emerge from is
is not the case for a Bitter disc. As such, the current defined to be the north pole. Much stronger magnetic
term must be replaced with terms discussing the fields can be produced if a "magnetic core" of a soft
cross-sectional area of the disc and the current ferromagnetic (or ferrimagnetic) material, such as
density. The equation for the on-axis magnetic flux iron, is placed inside the coil. A core can increase the
density of a Bitter disc becomes much more complex magnetic field to thousands of times the strength of
as a result. The differential flux density is related to the field of the coil alone, due to the high magnetic
the current density and the differential area. The permeability μ of the material. This is called a
introduction of a “space factor” must be included to ferromagnetic-core or iron-core electromagnet.
compensate for variations in the disc related to However, not all electromagnets use cores, and the
cooling and mounting holes. very strongest electromagnets, such as
superconducting and the very high current
Round and Rectangular Flat-Faced Electromagnets electromagnets, cannot use them due to saturation.
Round and Rectangular Flat-Faced Electromagnets The factor limiting the strength of electromagnets is
are available in a variety of sizes. Flat-Faced magnets the inability to dissipate the enormous waste heat, so
should only be used on flat, smooth material where more powerful fields, up to 100 T, have been
the entire magnet face is in contact. They can be used obtained from resistive magnets by sending brief
in manually operated or automated applications. pulses of high current through them; the inactive
Magnets listed utilize 12 volt D.C. current (24VDC period after each pulse allows the heat produced
and 110VDC are available by request). during the pulse to be removed, before the next pulse.
Standard Leads are 24" The most powerful manmade magnetic fields have
Dimensions are in inches been created by using explosives to compress the
Pounds pull ratings are maximum on low carbon magnetic field inside an electromagnet as it is pulsed,
steel at magnetic saturation. using explosively pumped flux compression
Contact us at 800-747-7543 if you don't see what generators.
you're looking for in this brief listing
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4. International Journal of Industrial Electronics and Electrical Engineering, ISSN(p): 2347-6982, ISSN(e): 2349-204X
Volume-5, Issue-8, Aug.-2017, http://iraj.in
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Electromagnets and their Applications