Magnet, its Properties and Magnetic domains | video in HINDI | EduPoint

Описание: In this Physics video lecture in Hindi we discussed about magnet, its properties and the reason behind magnetism. During this video tutorial we talked about natural and artificial magnets, whereas artificial magnets can be catagorised as permanent and artificial magnets. We also discussed about ferromagnetic, diamagnetic and paramagnetic substances. We also saw that ferromagnetic substances contain magnetic domains which act as units of magnet. Ferromagnetic substances contain domains whereas paramagnetic and diamagnetic substances do not contain domains, hence only ferromagnetic substances are attracted towrards a magnet and only those can be used to make a magnet.

Some properties of magnet are :
(i) Attractive property :- A magnet can attract magnetic substances like iron, steel, nickel etc.
(ii) Inductive property :- When a magnetic material is placed near a magnet it acquires magnertism.
(iii) Directive property :- A bar magnet, when suspended freely, aligns itself approximately along geographical north-south line.
(iv) Like poles repel each other and unlike poles attract each other.
(v) Magnetic poles exist in pairs.

Some related topics :
Magnetic Pole : The preferred region of attraction near the two ends of a magnet, where the magnetic force due to a magnet is maximum, are called the poles of that magnet.
In S.I., its unit is A m or ampere-meter.

Coulomb's law in magnetism : It states that the magnetic force between two magnetic poles is directly proportional to the product of the magnitude of pole strengths and inversely proportional to the square of the distance between them.
F ∝ m_1 m_2
And F ∝ 1/r^2
Hence, F ∝ (m_1 m_2)/r^2
or, F = μ_0/4π (m_1 m_2)/r^2
where, μ_0 is called absolute permeability or permeability of free space and μ_0/4π = 10-7 Wb A-1 m-1

Magnetic pole strength : A magnetic pole is said to be of unit strength, if it repels an equal and similar pole with a force of 10^-7 N, when placed in vacuum (or air) at a distance of one meter from it.


Magnetic length : The distance between the two poles of a bar magnet is called the magnetic length of that magnet.
Magnetic length is a vector quantity and its direction is from S-pole of the magnet to its N-pole. It is denoted by 2 l .

Magnetic dipole: An arrangement of two magnetic poles of equal and opposite strengths separated by a finite distance is called a magnetic dipole.

Magnetic dipole moment : The product of the strength of either pole and the magnetic length of the magnet is called magnetic dipole moment.
It is a vector quantity and is represented by M ⃗. Its direction is from S-pole to N-pole.
M ⃗ = m ( 2 (l ) ⃗ )
In S.I., its unit is A〖 m〗^2 or Ampere〖 meter〗^2

Magnetic field :- The space around a magnet ( or a conductor carrying current ), in which its magnetic effect can be experienced, is called the magnetic field.

In S.I., its unit is tesla (T)
1 tesla = 1 newton 〖ampere〗^(-1) 〖metre〗^(-1)
1 tesla = 1 weber 〖metre〗^(-2)

Magnetic field lines :- A magnetic field line is a path along which an isolated north pole will tend to move, if it is free to do so.


Few properties of magnetic field lines :-
The magnetic field lines are closed continuous loops extending through the body of a magnet.
Outside the body of the magnet, the magnetic field lines run from north-pole to south-pole of the magnet.
The tangent to the magnetic field lines at a point gives the direction of the magnetic field at that point.
No two magnetic field lines can intersect each other.
The relative closeness of field lines gives the idea of the strength of the magnetic field.


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Arijit Daripa
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