Magnetic Terms - Magnetic Material - Properties of Magnet

Magnetic Terms, Magnetic Material and Properties of Magnet

Magnet : The substance which attracts a magnetic material towards it , is known as magnet.

Magnetism is the force exerted by magnets when they attract or repel each other.

Classification of magnets: Magnets are classified into two groups.

1. Natural magnets: Lodestone (an iron compound) is a natural magnet which was discovered centuries ago.
2. Artificial magnets: Artificial magnets are magnets made by people .There are two types of artificial magnets. Temporary and permanent magnets.

Temporary magnets or electromagnets: The magnet which attains the magnetic properties for short periods is called temporary magnets. It is made by winding a coil of insulated wire round a soft iron core. When a current is passed through the coil, the magnetic field produced by the current magnetizes the soft iron core. The soft iron core loses all the magnetism when the current is switched off.

Permanent magnets: The magnets which retains the magnetic properties for longer periods is called permanent magnets. If steel is substituted for soft iron in the same inducing field as in the previous case, due to the residual magnetism, the steel will become a permanent magnet even after the magnetizing field is removed.

Classification of magnetic substances Materials can be classified into three groups as follows.

1. Ferromagnetic substances: Those substances which are strongly attracted by a magnet are known as ferromagnetic substances. Some examples are iron, nickel, cobalt, steel and their alloys.
2. Paramagnetic substances: Those substances which are slightly attracted by a magnet of common strength are called paramagnetic substances. Their attraction can easily be observed with a powerful magnet. In short, paramagnetic substances are similar in behavior to ferromagnetic materials. Some examples are aluminum, manganese, platinum, copper etc.
3. Diamagnetic substances: Those substances which are slightly repelled by a magnet of powerful strength only are known as diamagnetic substances. Some examples are bismuth, sulphur, graphite, glass, paper, wood, etc. Bismuth is the strongest of the diamagnetic substances.

Magnetic terms and properties of magnet:

Magnetic fields: The magnetic field is the area around a magnet in which there is magnetic force.

Magnetic lines: Magnetic Lines of Force is a an imaginary line representing the direction of magnetic field.

Magnetic axis: The imaginary line joining the two poles of a magnet are called the magnetic axis.

Magnetic neutral axis: The imaginary lines which are perpendicular to the magnetic axis and pass through the center of the magnet are called the magnetic neutral axis.

Properties of a magnet: 

Attractive property : 

    A magnet has the property of attracting magnetic substances (such as iron, nickel and cobalt) and its power of attraction is greatest at its poles.

Directive property: 

    If a magnet is freely suspended, its poles will always tend to set themselves in the direction of north and south.

Induction property: 

    A magnet has the property of producing magnetism in a nearby magnetic substance by induction.

Poles-existing property: 

    A single pole can never exist in a magnet. If it is broken into its molecules, each molecule will have two poles.

Demagnetising property: 

    If a magnet is handled roughly by heating, hammering, etc. it will lose its magnetism.

Property of strength: 

    Every magnet has two poles. The two poles of a magnet have equal pole strength.

Saturation property: 

    If a magnet of higher strength is further subjected to magnetization, it will never acquire more magnetization due to its being already saturated.

Property of attraction and repulsion: 

    Unlike poles (i.e. north and south) attract each other, while like poles (north/north and south/south) repel each other.

Assumed physical properties of magnetic lines of force: 

    The lines of force always travel from the north to the south pole outside the magnet through air and from the south to the north pole inside the magnet.

    All the magnetic lines of force complete their circuit (forma loop).

    The magnetic lines do not cross each other. The lines of force travelling in one direction have a repulsive force between them, and, therefore, do not cross.

Magnetic shielding: 

    Electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. Electromagnetic shielding that blocks radio frequency (RF) electromagnetic radiation is also known as RF shielding.