Magnets can be natural or artificial. Natural magnets are found in nature, like lodestone, while artificial magnets are human-made from materials like iron, nickel, or cobalt. Magnets have several properties including attraction, repulsion, and the creation of magnetic fields visualized using iron filings. The strength of a magnet's field is measured by magnetic flux and flux density. Materials have varying magnetic permeability depending on their ability to be magnetized. Molecular theory explains magnetism at the level of magnetic domains within materials.

2. MAGNETISM
• Magnets are objects of stone , metal or
other material which have the property of
attracting metals like iron , cobalt and nickel .
The attracting property of a magnet is called
magnetism and is either natural or induced .
• It was first found in magnesia hence named
magnetite or magnet.
• Magnets can be classified as natural magnets
(magnetite) and artificial magnet.

3. • Magnets found in the nature are called natural
magnets . They are permanent magnets i.e. ,
they will never lose their power These
magnets are found in different places of the
earth in the sandy deposits . Lodestone called
magnetite is the ore of iron is the strongest
natural magnet . Minerals like Pyrrhotite ( Iron
Sulphide ) , Ferrite and Coulumbite are also
natural magnets .
Natural Magnets

4. • Artificial Magnets made by people in the
laboratory or factory are called artificial magnets
. These are also known man made magnets ,
which are stronger than the natural magnets .
Artificial magnets can be made in various shapes
and dimensions . Bar magnets , U - shaped
magnets , horseshoe magnets , cylindrical
magnets , disc magnets , ring magnets and some
examples of artificial magnets . Artificial magnets
are usually made up of iron , nickel cobalt , steel ,
etc.
Artificial Magnets

5. • MAGNETIC PROPERTIES
– Attractive property
– Reflective property
– Directive property
• Magnets attract objects of iron, cobalt and nickel
• The force of attraction of a magnet is greater at
its poles than in the middle.
• Like poles of two magnets repel each other.
• Opposite poles of two magnets attracts each
other.

6. Magnetic Field
Magnets show repulsion or attraction force around
itself. This area affected from the force of magnets
called magnetic field.
We cannot see magnetic field necked eye. However, if
we put a sheet on the magnet and put some iron
filing on this sheet we can easily observe the
magnetic field around the magnet with the shapes of
the iron filling. The shapes of magnetic field lines
showed in the picture given below;

7. • You can observe from this experiment that the iron filings
are arranged in the form of curved patterns around the
magnet.
• the space around the bar magnet where the arrangement
of iron filings exists , represents the field of influence of the
bar magnet . It is called the magnetic field .
• Magnetic field is defined as the space around a magnet in
which its magnetic effect or influence is observed .
• It is measured by the unit tesla or gauss ( 1 tesla = 10,000
gauss ) .

8. • Magnetic Flux
• Total number of magnetic lines of force
passing through a given space of field is called
magnetic flux. Its unit is Maxwell who is very
small practical unit is Weber, which equals 108
Maxwell.

9. Magnetic flux density
• It is the density of magnetic lines of force, or magnetic flux
lines, passing through a specific area. It is measured in units
of tesla.
Flux Density (denoted by ‘B’)
• The number of magnetic force lines passing in unit area, any
where in the magnetic field and in right angle to the magnetic
field is called flux density. Its unit is Webber/Sq. meter=TESLA
• B = Total Flux (Ø) / Total area of flux (A) Wb/Sq
meter
Magnetising Force (Strength of magnetic field- denoted by ‘H’)
• It is the strength of a magnetic field of magnet, with
which it can magnetize another magnetic substance. Its unit is
Ampere / Meter or “Oersted”

10. • Unit Pole Strength:The quantity of magnetic flux in
Webers released by a pole is called pole strength.
When pole releases 1 Weber magnetic flux, it is said to
have 1 unit pole strength or unit pole strength.
• Permiability
• It is the property of a magnetic material to allow
(permit) the magnetic line of force to pass through is
called permeability. It can also defined the ratio of
conducting power of a medium for magnetic flux with
that of vacuums. It is denoted by symbol ‘’ (mue). ‘’
for air is 1.
•
•  = B (applied flux density) / H (Magnetic field
str. any point in the medium)

11. • Magnetic permeability is the ability of a material to respond to
how much electromagnetic flux it can support to pass through itself
within an applied electromagnetic field.
In other word magnetic permeability of a material is the degree of
magnetization capability.
• Magnetic permeability is expressed in μ that is a Greek Letter. In
1885, Mathematician Oliver Heaviside had termed magnetic
permeability as μ.
• Unit of Electromagnetic Permeability
• The unit of Electromagnetic Permeability is Henry/meter or
Newton/sq-ampere.
• Permeability in Free Space
• Permeability in free Space is denoted as μ0. Its value is 4ᴫ × 10-
7 H/m (or permeability in vacuum is absolute permeability) . This
value of permeability is taken as standard value that is treated as
permeability constant. μr=5 for glass and 1 for air.
• μ= μ0+μr value of μ0 is constant (4ᴫ × 10-7 H/m)
• vallue of μ1 is variable
• Ferro magntic material have μ1>>1

12. Intensity of Magnetisation
It is the measure of intensity to which a magnetic
substance can be magnetised using a magnetic field. It is
denoted by ‘I’ unit is weber/Sq meter.

13. • Diamagnetic matters: If the relative
permeability f the matter is a little bit lower
than 1 then we say these matters are
diamagnetic.
• Paramagnetic matters: If the relative
permeability of the matter is a little bit higher
than 1 then we say these matters are
paramagnetic.
• Ferromagnetic matters: If the relative
permeability of the matter is higher than 1
with respect to paramagnetic matters then we
say these matters are ferromagnetic matters.

14. Susceptibility (K)
• Ratio of intensity of magnetisation to the
magnetising force is susceptibility
• (K = I / H, where K is susceptibility, I is intensity of
magnetisation and H is magnetising force)
Magnetism as a form of energy
• Like electricity, magnetism is also a form of
energy. Magnetic energy can be converted to
other form of energy like mechanical or electrical
energy with, the use of certain equipment’s /
machines.

15. Molecular Theory of Magnetism
Molecules of all the materials, irrespective of
magnetic or non-magnetic material, are small magnets i.e.
have N and S poles in themselves. In a material, which is not
a magnet, these molecules are arranged in haphazard way,
so the effect of magnetism in the molecules are cancelled
out by each other (see figure)

16. But in a magnet, or when a magnet substance is magnetized
the molecules are arranged in an orderly manner so that the
effect of them are added together to form a magnet.
When an Iron bar is placed under influence of a
magnetizing force, the molecules in Iron bar arranges
automatically to an orderly manner. This is called
magnetization. When the molecules are fully arranged in
such way, it said to be at a magnetic saturation or, the
maximum degree of magnetization is called magnetic
saturation.