|These are found naturally and they are irregular in shape.
|These are made by man which is a definite shape based on the usage.
|The strength of the magnet is natural and it is difficult to change.
|Artificial Magnet is made with specific strength as required.
|Natural Magnets are long-lasting, i.e that does not lose their magnetic power.
|It loses magnetic strength with time
|They have less usage
|They are usage day to day applications.
This note is written for the Tnpsc for the topic “Magnetism”, in the general studies.
This note is prepared from Tamil Nadu, Samacheer Kalvi Books.
Natural magnet and Artificial magnet
Magnets are materials such as stone, tools,s or metal that have the property of attracting metals such as Nickel, Iron, Cobalt. This attractive property of materials is called Magnetism.
Magnetism is of two types: Induced or Natural.
The branch of physics that studies the property of a magnet is also called Magnetism. The usage of the earliest Magnet was found in Asia minor called Magnesia.
It is believed the Chinese knew about the Magnets as early as 200 BC. Chinese also used a magnetic compass for navigation in 1200 A.D.
Today magnets are used everywhere from electricity production, engines, elevators, speakers, etc.
Classification of Magnets
There are two kinds of Magnets: Natural magnets and Artificial magnets.
The magnets that are found naturally are termed Natural Magnet. Natural magnets are Permanent Magnets, which means they do not lose their magnetic power.
Natural Magnets are found in different places such as sandy deposits. The strongest natural magnet is Lodestone called Magnetite or Iron oxide which is the ore of iron.
Some other natural magnets are Minerals such as Pyrrhotite or Iron Sulphide, Ferrite, and Columbite. There are three types of Iron ores Hematite(69% of Iron), Magnetite (72.4% of Iron), and Siderite (48.2% of Iron).
Among the Iron ores, Magnetite (Fe2O4)has the strongest Magnetic property.
Magnets that are man-made in the labs, companies are called Artificial Magnets or Man-Made Magnets.
Artificial magnets normally have stronger magnetic fields than Natural Magnets.
There are various shapes, and artificial magnet examples are made such as bar magnets, U-Shaped Magnets, Horsehoe Magnets, Cylindrical Magnets, disc magnets, ring magnets, and electromagnets.
The artificial magnets are made of Nickel, cobalt, steel, iron, etc, and made of alloys such as Neodynium and Samarium.
The magnetic field is defined as the space around a magnet in which its magnetic effect or influence is noticed and it is measured by unit tesla or gauss ( 1 tesla = 10,000 gausses).
Tracing the magnetic field
A compass needle also is known as a plotting compass or magnetic needle consist of a tiny pivoted magnet in the form of a pointer, that rotates freely in the horizontal plane.
The ends of the compass approximately point towards the North-South Direction.
Materials that are attracted to Magnetic forces are called Magnetic materials and materials that are not attracted toward Magnetic forces are called non-magnetic materials.
Magnetic materials can be magnetized to form Permanent magnets. Magnetic materials are of two types one is magnetically soft materials and magnetically hard materials. Magnetically hard materials require a strong magnetic field to get magnetized.
It is because the different atomic structures behave differently when placed in a magnetic field.
Classification of magnetic materials
Materials are classified based on their behaviour in the magnetic fields such as:
Classification of Magnetic materials: Natural magnet and Artificial magnet
The Diamagnetic materials have the following characteristics:
Diamagnetic materials, when suspended in an external uniform magnetic field, will align perpendicular to the direction of the magnetic field.
Diamagnetic have a tendency to move away from the stronger part to the weaker part when it’s suspended in a non-uniform magnetic field. Diamagnetic get magnetized in the direction opposite to the magnetic field.
Examples: Bismuth, Copper, Mercury, Gold, Water, Alcohol, Air, and Hydrogen. The magnetic character of the Diamagnetic materials does not get affected by the external temperature.
Paramagnetic materials have the following characteristics:
When a Paramagnetic Material is placed freely suspended in a uniform magnetic field, it will align itself parallel to the magnetic field. They have the tendency to move from the weaker part to the stronger part when placed in a non-uniform magnetic field.
Paramagnetic materials get magnetized in the direction of the field.
Example: Aluminium, Platinum, Chromium, oxygen, manganese, solutions of salts of nickel and iron. The magnetic character of Paramagnetic materials gets affected by external temperature.
When a suspended, Ferromagnetic Material is placed in the uniform magnetic field it will align itself in parallel to the direction of the magnetic field.
When a suspended Ferromagnetic Material is placed in the non-uniform magnetic field it will move quickly towards the stronger part from the weaker part.
Ferromagnetic Material strongly gets magnetized in the direction of the field. Examples: Iron, Cobalt, Nickel, Steel, and its alloys.
The magnetic character gets affected by the external temperature. Ferromagnetic Material, when heated becomes Paramagnetic Materials.
The temperature at which Ferromagnetic materials become Paramagnetic material is called Curie Temperature. (2)
These are man-made magnets, made from magnetic materials. These are commonly made by magnetizing iron or steel alloys electrically.
“Artificial magnets are made by stroking a magnetic material with magnetite or with other artificial magnets”. (Wikipedia) (Tamil Nadu Government #)
These kinds of processes are called Magnetisation.
“The magnetisation is a process in which an object is turned to the permanent or temporary magnet by exposing it to an external maternal magnetic field”. (Tamil Nadu Government #)
Depending upon their magnetic power retaining nature, the artificial magnets are classified into two types, one temporary and another one is a permanent magnet.
Temporary Magnets are made by an external magnetic field. Temporary Magnets lose their magnetic property as soon as the external magnetic field is removed.
Temporary Magnets are made from soft iron. Soft iron acts as Magnets by the influence of an external magnetic field produced in a coil of wire carrying electricity.
Soft iron loses its magnetic property as soon as the electricity is stopped.
Examples: Magnets used in Crane, Electric Bell.
Permanent Magnets are artificial magnets that retain their magnetic property even after the external magnetic field is taken off. The Permanent magnets are made from hardened steel and alloys of some metals.
Generally, the alloy used to make permanent magnets are ALNICO (An alloy of aluminium, nickel, and cobalt).
Examples of Permanent Magnet usage are Refrigerator, bar magnet, speaker magnet, fridge, magnetic compass, etc.
Neodymium magnets are the strongest magnets on the earth. Alnico cow magnets are used to attract sharp iron objects such as wire, nails ingested by animals grazing, which also damage its digestive tract.
Cow magnets factsIt is used by farmers to prevent Hardware disease called Bovine Traumatic Reticuloperitonitis, as Cow might swallow nails, wire etc. This magnet of the size of the finger is placed inside a bolus gun and it is essentially a long tube that ensures the magnet goes down the cow’s throat. This magnet settles inside the reticulum collecting any pieces of metals.
The Magnetic properties lose in the following ways:
Leaving the magnet unused for a long time. The endless hammering of the magnetic material. Releasing magnet from a height. Roasting magnet to great temperature. Giving a variable current in a coil that encircles the magnet. Incorrect storage of the magnet.
Uses of Magnet
In ancient days, magnets are used as ‘Direction Stone’, used for Navigation. Used to dynamos, to generate electricity. Electromagnets used in electric bell, etc. Used in Motors. Used in speakers, microphones, etc
The powerful electromagnet used in Maglev trains. In industries, magnetic conveyor belts are used to sort magnetic substances from scraps. Used in the computer as storing devices such as hard disks.
Used in Atm card, Magnetic strips which are made of tiny iron-based magnetic particles in thin plastic film. MICR number printed on the cheque in Banks. Tip the screwdriver with a magnet, to attract the screw.
MRI (Magnetic Resonance Imaging) is used to scan the internal organs in hospitals.
Other Facts on Magnetism
Pigeons have magnetite in their beak, which helps in navigation by sensing the magnetic field of the earth such a sense is called magneto-reception.
The most powerful magnet in the universe is a Neutron Star called Magnetar (Magnetic Neutron star) in the Milky Way, with a diameter of 20km and mass of 2 to 3 times of the Sun.
- Tamil Nadu Government. 8th Science Book. First Edition ed., vol. III, Chennai, Tamil Nadu Text Book Corporation, 2019. 3 vols. Samacheer Kalvi, http://tnschools.gov.in/media/textbooks/8th_Science_EM_Combined_05-03-2020.pdf. Accessed 27 10 2020.
- Britannica, and Gloria Lotha. “Curie point.” Britannica, Encyclopædia Britannica, Inc, 20 July 1998, https://www.britannica.com/science/Curie-point. Accessed 28 10 2011.