Magnetic Substances and molecular theory

Magnetic substances

The substances that are attracted by a magnet are called magnetic substances. Example : Iron, nickel, cobalt, steel etc.

Nonmagnetic substances :

The substances that are not attracted by a magnet are called nonmagnetic substances. Example : Paper, glass, water, common salt, plastic etc.

In a sense, all substances have magnetic properties. Howerer the degree of magnetism exhibited by them differs. Based on their properties when brought under the influence of powerful magnetic field, They are classfied into three groups –

Diamagnetic,

Paramagnetic and

Ferromagnetic substances.

Do You Know ?

Experiments have revealed that the ability of paramagnetic substance to get magnetised goes on increasing as we go on cooling it. This abillity goes on decreasing as its temperature increases and at one specific temperature it altogether vanishes, Can you guess why ?

A diamagnetic material shows no magnetic peoperty. For example, bismath. Antimony. Lead, gold and water, Diamagnetic materials show feeble magnetism when placed in a strong magnetic field.

Paramagnetic materials show some magnetism in a magnetic field. Examples are aluminium, platinum. Chromium, copper and sulphate.

Ferromagnetic materials have good magnetic peoperty and are easily magnetized by external magnetic fields Examples are iron, nickel and cobalt.

Molecular theory

Molecular theory is the first theory which made an attempt ot explain the phenomenon of magnetism. It attempted to find the reason for the magnetic property of substances at the molecular level. According to this theory, every molecule of a magnet behaves like amagnet. Every molecular magnet has two poles, namely, north pole and south pole, Molecular magnets have the ability to rotate around their centres. All substances, even the unmagnestised ones are made up of such molecules.

How does molecular theory explain the properties of a magnet ?

Observation : Certain substances do not exhibit magnetic peoperties whereas some other substances do.

Explanation : All substances are made up of molecules that behave like magnets. In nonmagnetic substances, the molecules are scattered rendomly in all directions. Hence the effect of poles of molecular magnets cancel each other. Hence they do not exhibit magnetic properties. In a magnet, all ther molecular magnets are arranged in the same direction parallel to each other. Hence the effect of poels of molecular magnets add up. Therefore magnets exhibit magnetism.

Molecular Theory

 Explanation : Whenever a magnet a dropped, the uni-directional arrangement of molecular magnets gets disturbed. Kinetic energy of molecular magnets increases when heated. Therefore, when heated, the molecular magnets attain a disorderly arrangement.

The knowledge of magnetism has gone beyond the framework provided by molecular theory. Now we know that it is more complicated than what it was thought to be. It is now established that each and every proton and electron of an atom has magnetic property. The molecular magnetism is a resultant of all these magnetic properties. Yet, the molecular theory has not lost its importance. Why ? It is because,it interprets most of the phenomena that are associated with magnetism.