Methods of Magnetisation and Demagnetisation - Fun with Magnets - CBSE Class 6 Science Video Lecture

double-dutch method
place a steel bar to be magnetized on to
bow magnets as shown here
now place opposite poles of two strong
magnets at the middle of the steel bar
as shown here move the magnets towards
the opposite ends of the specimen
keeping the magnets inclined on reaching
the opposite ends
lift the magnets and place them back to
their respective original positions
repeat the process the polarities
developed at the ends are opposite to
the polarity of the pole used for
magnetization play some iron nails on
the table now bring the steel bar near
the eye nails the steel bar attracts the
nails showing that it has the quired
magnetism
introduction magnetization is the
process by which a magnetic substance
attains magnetism temporarily or
permanently the methods used to
magnetize a magnetic substance are
single touch method double touch method
electrical method of magnetization T
magnetization is the process of removing
the magnetic property of a magnet the
magnetism of a magnet can be totally or
partially destroyed in the following
ways by rough handling by heating by
induction by passing electricity
single touch method place a soft
timepiece a B to be magnetized on a
table take a bar magnet and place one of
its folds on the soft iron piece as
shown here stroke the soft iron piece
with the bar magnet when the magnet
reaches B lift it and place it back to
the position a and repeat the process
several times the upper side of the soft
iron gets magnetized now turn the soft
iron bar as shown here and magnetize the
lower side in the same manner the point
a will get the same polarity as the Pole
of the magnet touching it and the other
end of the bar will attain the polarity
opposite to that of the magnetizing Pole
test for magnetism play some iron nails
on the table now bring the soft iron
piece near the iron nails the soft
timepiece attracts the nails showing
that magnetism is induced in it
double-dutch method
place a steel bar to be magnetized on
two bar magnets as shown here
now place opposite poles of two strong
magnets at the middle of the steel bar
as shown here move the magnets towards
the opposite ends of the specimen
keeping the magnets inclined on reaching
the opposite ends
lift the magnets and place them back to
their respective original positions
repeat the process the polarities
developed at the ends are opposite to
the polarity of the pole used for
magnetization play some iron nails on
the table now bring the steel bar near
the eye nails the steel bar attracts the
nail showing that it has the quired
magnetism
Electrical method of magnetization the
given bar that is to be magnetized is
placed inside a long coil of insulated
copper wire the copper wire is connected
to a source of direct current as shown
here
when the circuit is closed a strong
direct current passes through the coil
of the insulated copper wire and the bar
becomes a magnet the polarity of the rod
depends upon the direction of the
current
if the bar is viewed from one end and
the current is found to be flowing in a
clockwise direction then that end will
attain South polarity
if the current appears to be flowing in
an anti-clockwise direction then that
end attains North polarity if it is a
steel bar it becomes a permanent magnet
if the bar is a soft iron bar then it
becomes a strong bar magnet and is
called an electromagnet this
electromagnet ceases to be a magnet as
soon as the current is stopped
you
methods of demagnetization the magnetic
property of magnet can be totally or
partially destroyed by rough handling by
heating by induction or by passing
electricity
click on each method for more
information
hammering dropping and rough handling of
the magnet candy magnetized the magnet
a magnet loses its magnetism if it is
heated above a certain temperature
called its Curie point the Curie point
for iron is 770 degree Celsius and that
of Steel is 880 degrees Celsius the
Curie point for nickel is 358 degrees
Celsius and that for cobalt is 1120 one
degree Celsius
if two magnets are
side-by-side with similar poles together
each induces opposite polarity in the
other as a result the magnets lose
magnetism to avoid the self
demagnetization the magnets are placed
in pairs side by side with their unlike
poles together as shown here
by passing electricity plays the given
bar that has to be demagnetized inside a
long coil of insulated copper wire in
the east-west direction connect the
copper wire to a source of alternating
current as shown here switch on the
circuit
now slowly reduce the current to zero
the magnet loses its magnetism as
alternating current changes direction
continuously this change in direction of
current disturbs the alignment of
molecular magnets resulting in
demagnetization