Magnets are material or object which creates magnetic field. The magnets
could be naturally occurring material but these could also be formed in
laboratories. The magnetic field and the electric field are synonymous
to each other, as a varying electric field could produce a magnetic
field and the varying magnetic field could produce electric field.
this section of magnets, we will learn about the magnets which could be
formed by the use of the electric field. These types of magnets are
termed as Electromagnets, as they are produced by the application of the
An electromagnet can be formed, simply, by the use of a coil of wire. The coil of wire, usually, has an iron core wounded around it. But instead of using iron core one could also use air core and the result is a solenoid. When the coil of wire is connected to a DC voltage or current source, it becomes energized and in turn creates a magnetic field like a permanent magnet. This is known as Electromagnet. The magnetic flux density of the electromagnet is proportional to the current flowing through the wire of the coil or electromagnet.
The direction of the current through the coil of the electromagnet decides the polarity of the magnetic field. The north pole of the so formed electromagnet can be determined by using right hand rule.
Right Hand Thumb Rule: Hold the coil of the electromagnet with the fingers of your hand. The fingers must be in the direction of the flow of the current in the coil. In this case your thumb is pointing in the direction of the magnetic field produced by the electromagnet, so north would come out of the electromagnet in the direction of your thumb.
DC electromagnets create a constant magnetic field with constant polarity and are principally used to pick up or hold objects.
When connected to an AC voltage or current source is connected to the coil of electromagnet, the electromagnet will be changing its flux density with respect to the fluctuations in the current. Due to the change in the direction of the AC every half cycle the polarity of the electromagnet will also changes. These types of electromagnets are used for demagnetizing the electronic objects (like TV screens, audio tapes, vcr tapes, etc). or to hold objects. However, the magnetic flux of the field produced by the AC voltage of the same value as that of the DC voltage is less due to the inductance of the electromagnet. The inductance would reduce the actual AC current that will flow through the coil.
Advantages of Electromagnets:
- The electromagnet has the ability to control the strength of the magnetic flux density. The strength of the magnetic flux density of an electromagnet can be controlled by the controlling the magnitude of the current flowing through the coil.
- The electromagnet has the ability to control the polarity of the field. The polarity of the magnetic field can be control by the direction of the flow of current through the coil.
- The electromagnet has the ability to control the shape of the field. The shape of the magnetic field is determined by the shape of the core used in the electromagnet on which the coil is wounded.
In 1820, Danish scientist Hans
Christian Oersted discovered that the electric currents could create
magnetic fields. The first electromagnet was invented by a British
scientist William Sturgeon in 1824. He used a iron piece of horseshoe-shape for his first electromagnet. He wrapped the horse shoe with bare copper wire approximately of around 18 turns and has varnished the iron to
insulate it from the copper wire windings.
He then connects the
windings to the electricity so that the electric current was allowed to pass
through the coil. As soon as current is passed through the windings, it lead to the magnetization of iron and this attracted other pieces of iron. As soon the electric current was stopped, it loses its magnetization. Sturgeon
displayed the power of the electromagnet by showing that although the
iron piece is weighing very less (roughly 200 grams).
When the current of a single-cell
battery was applied it could lift objects roughly upto 4 kilos. Although the sturgeon electromagnet
was very weak still this experiment paved a new beginning and in 1827, a
US scientist Joseph Henry improved and helped popularize the electromagnet. He used silk thread insulated wires so that he could
wind multiple layers of wire on the iron cores. It creates powerful
magnet with thousands of turns of wire, which could support heavier
objects (around 936 kg).
The Electromagnetic Induction is the opposite
effect of the electromagnet. When a conductor passes through a magnetic
field then a current is induced in it, this phenomenon is known as
electromagnetic induction. This is the basic principle behind the
working of the electric motor, generators, transformers, etc.
The conductor should either move
in the magnetic field, if the magnetic field is constant or the
magnetic field should be varying. The current would not induce on a
stationary conductor in the constant magnetic field.
The Electro Permanent Magnet has the benefits of both
the permanent magnet and the electromagnet. The electromagnet is placed
in between the permanent magnet as shown in figure below.
can be seen from the diagram, the magnetic field of both the magnets
are aligned and produces a strong magnetic force. Now see what happens
when the polarity of current is reversed in the electromagnet. As shown
in the diagram below, we see that the magnet field produced by both the
field tends to cancel each other and hence the overall magnetic field
due to this arrangement is zero. This type of arrangement is used in
attaching and detaching the objects like iron.
The Electromagnetic Pulse or EMP is the sudden outburst of electromagnetic radiations due to varying magnetic and electric field. It is harmful for an electronic circuit and destroys the equipment. This moves with a frequency of particular range. It propagates like a wave hence the name electromagnetic pulse. It is also known as transient disturbance.
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