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Std XII | KARNATAKA STATE BOARD | Physics | Introduction to Magnetism

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Hello students today we will discuss the
concept of magnetism and matter before going to the concept of magnetism and
matter I would like to give you certain key points regarding the magnetism that
is history of magnetism once Magnus was herding his sheep in an area of northern
Greece called magnesia suddenly both the nails of his shoes and the metal tip of
his staff became firmly stuck to the large black rock on which he was
standing he was very curious to know the fact behind it therefore to find the
source of attraction he dug up the earth and he finds lodestone this is how the
lodestone looks like a lodestone which contains magnetite a natural magnetic
material fe3o4 students keep in mind again a lodestone
which contains magnetite which is nothing but a natural magnetic material
fe3o4 okay fine so the directional property of magnet was also known since
Asian times that is a freely suspended magnet and the magnet which placed on a
piece of cork allowed to float in still water always pointed in the north-south
direction this is how we can recognize the directional property of the magnet a
freely suspended magnet and the magnet which placed on a piece of cork on float
in still water always points in not to the south direction okay so they have
also used this magnets in many application one of the application we’ll
see now you can look at the image the image is an chariot with that a magnetic
Idol is suspended the craftsmen built a chariot on which they placed a
netic figure which swelled around so that the finger of the statue ate on it
always pointed south with this chariot Hong t troops were able to attack the
enemies from the rear in thick fog and to defeat them this was one of the
application in the earlier days using the magnets and the latest science
suggests that moving charges or electric currents produce magnetic field moving
charges or electric currents produce magnetic fields this discovery was
credited to the scientists arrested am pure biota and sovereign dear students
now we’ll discuss the common ideas regarding the magnetism that is the
first one is the art behaves as a magnet with the magnetic field pointing
approximately from geographic South to the geographic north what does that mean
on the whole we can treat the art as a magnet where the magnetic field pointing
approximately from geographic South to the geography not next when a bar magnet
is freely suspended it points in the north-south direction this property you
know when a bar magnet is freely suspended it always points in what north
and south direction okay the tip which points the geographic
north is called the North Pole and the tip which points the geographic south is
called the South Pole you can observe the tip which points the geographic
north is the North Pole and the tip which points the geographic south is
South Pole okay the next point is like in electrostatics here also you can get
the properties like poles repulse each other what does that mean
if you bought two bar magnets of simples if you bought two bar magnets of simples
each other those two bar magnets tend to repel from one another why is it so
because between those two same poles repulsive force exists in the same way
unlike poles attract each other that means if you bought two bar magnets of
opposite poles those two bar magnets always attract each other and that is
because of the attractive force exist between the opposite poles so that on
the whole I can conclude like pole ripples each other and like pole
attracts each other and the next point is magnetic monopoles do not exist what
does that mean magnetic monopoles do not exist which is nothing but if you cut a
bar magnet into n equal pieces if you cut a bar magnet into n equal pieces
each one will be having both South and the north poles that means if you
consider a bar magnet and make it into n slices n number of slices each slices
what you have obtained will be always faciliate with the two poles that is not
Pole South Pole not pulse output not pulse output therefore we can say that
magnetic monopoles do not exist okay the next point is it is possible to make
magnets out of iron and it’s alloys yes we can manufacture magnets with the help
of iron and it’s alloys for example the manufacture of all nickel magnets uses
iron and it’s alloys Alico is nothing but what aluminium nickel and cobalt
okay the further discussions will be in the
next module till then keep learning thank you

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