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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.

In 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 electric field. 


What Are Electromagnetic Waves?

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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.  

Magnetic Field

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.

Right Hand Grip Rule

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:
  1. 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.
  2. 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.
  3. 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.

History of Electromagnets

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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).

Electromagnetic Induction

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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.

Electro Permanent Magnet

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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.
Permanent Magnet

As 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.

Electro Permanent Magnet
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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