Magnet and Principles of Magnetism

Signific

ance in our daily life

Magnet and Principles of Magnetism are one of those things that we come across in the daily course of our lives In our surroundings from television to mobile phones, cars, computers, medical equipment, MRI machines, toys, credit cards, Motors and Generators, Transformers, Relays, Electric bells and buzzers, Loudspeakers and headphones, Actuators, Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks, many scientific types of equipment such as mass spectrometers, Particle accelerators, Magnetic locks, magnetic levitation, used in a maglev train or trains Induction heating for cooking, manufacturing, and hyperthermia therapy and many more.

Magnets are incredibly important, particularly due to the relationship between electricity and magnetism. They play a very important role in our lives. Because of their magnetic qualities, magnets are put to various uses by the industries.

Depending on their magnetic qualities and composition while some of the magnets are visible in the devices that they are used, others are fitted inside the inner workings of the devices. Thus, it can be said that even if you can’t see the magnets they are silently doing their work unseen.

Since in many of the NDT methods Magnetic principles play a principle role hence this topic becomes important to learn as an NDT Technician.

History of Magnets

According to Greek legend, magnetism was first discovered about 4,000 years ago by a shepherd named Megnes, who lived in Megnesia, Greece. Megnes was herding his sheep through the mountains. Suddenly he noticed the ferrule of his stick and nails in his sandals got stuck to a rock(lodestone). The iron in his stick and nails had become attracted to the magnetic rock. The stone was named as magnetite, after the name of the shepherd or the country it was found in. It was also known as loadstone because of its attractive properties.

the early Chinese are believed to have first used them in magnetic compasses for navigation purposes. They realized magnets could direct needles and correlated with the north pole, and used that information to navigate. The early compasses were created with lodestone because modern magnets were not invented yet. Lodestone comes from the mineral magnetite and is the only naturally-occurring magnet. 

A reconstruction of an early Chinese compass. A spoon made of lodestone, its handle pointing south, was mounted on a brass plate with astrological symbols.

A MAGNETIC FIELD LINE OR MAGNETIC FLUX LINE shows the direction of a magnet’s force and the strength of a magnet

Type of Magnetic Materials

Di- magnetic:

• Diamagnetic materials are those whose atoms have only paired electrons.
• Hydrogen, ammonia, bismuth, copper, graphite
• diamagnetic substances are repelled by a nearby magnet.

Para magnetic:

• Paramagnetic substances are those which are attracted by magnets and when placed in a magnetic field move from weaker to stronger parts of the field.
• Aluminum, manganese, platinum are some examples of paramagnetic materials
• If a bar of paramagnetic material is suspended in between the pole pieces of an electromagnet, it sets itself parallel to the lines of force.

Ferromagnetic :

• Ferromagnetic substances are those which are attracted by the magnets and can also be magnetized.
• Iron, nickel, cobalt and their alloy
• Ferromagnetic materials are those materials which exhibit a spontaneous net magnetization at the atomic level, even in the absence of an external magnetic field.

Anti ferromagnetic

• These are similar to Ferromagnetic materials but the spin moments in each domain are aligned opposite to each other. Consequently, each domain results in a zero magnetization and hence a zero spontaneous magnetization.
• Examples: Chromium, Fe₂O_3, FeMn alloy, and NiO, etc.

Ferrimagnetic

• These are similar to anti-ferromagnetic materials, but the magnitude of one set is not equal to the magnitude of other sets of spins.
•  As a result, each domain results in a non-zero magnetization and hence a non-zero spontaneous magnetization of the whole sample. But the net dipole moment is always less compared to ferromagnetic net dipole moment.
• Example: Fe₃O₄

Hysteresis Loop

The hysteresis loop is a four-quadrant B-H graph from where the hysteresis loss, coercive force and retentivity of magnetic material are obtained.

Magnetic Permeability:

it is described as the ease with which materials can be magnetized. It is the ratio between the flux density and the magnetic field strength.

The reciprocal of permeability is reluctance, defined as the resistance of a material to changes in the magnetic field strength 

Electromagnetic Induction

Principally when current passes through a conductor, a magnetic field is formed in and around the conductor, this is called induced magnetic field and vice versa also occurs.

If the conductor has a uniform shape like a circular rod. The density of the external field is uniform at the same radial point along the length of the conductor.

At any point on the conductor, the magnetic field is the strongest at the surface of the conductor and decreases as the distance increases from the conductor surface.

A solenoid is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. The coil can be arranged to produce a uniform magnetic field in a volume of space when an electric current is passed through it. The term solenoid was coined in 1823 by André-Marie Ampère to designate a helical coil.

References’:

The significance of Magnets in Our Daily Lives

www.wikipedia.org

How Important is Magnet in Our Daily Life

https://byjus.com/physics/discovery-magnets/

Brainly.in – https://brainly.in/question/9678623#readmore

PTP magnetic particle testing classroom training Book

Cover Photo: https://www.exploratorium.edu/sites/default/files/f0233.gif