MAGNETISM
The word
“magnetism” originated from the city of Magnesia (now called Mania in Turkey)
where iron ores were discovered which had the property of adhering to each
other in lumps.
ELECTRO
MAGNETISM
Electromagnetism is the part of science
which deal with the relation between electricity and magnetism.
In the year 1819, Professor, Hans
Christian Oersted, university of Copenhagen, Demark, accidently discovered that
on passing a wire carrying current parallel to a magnetic needle, there was a
deflection in the needle, as if it was acted upon by a magnet. In this
experiment he concluded that every conductor carrying current is surrounded by
a magnetic field.
In 1845 Faraday showed with the help of
very powerful electromagnets that almost all substances were influenced by a
magnet to varying degrees. He suspended, by a long and fine suspension wire,
small bars of various solid substances between the poles that of strong
electromagnets, while switching on the current, he found that some of the
substances arranged themselves with their lengths parallel to direction of the field,
while the other set themselves in a direction at right angles to the direction
of the field.
MAGNETISM & ELECTROMAGNETISM
Magnetism
is a force filed that acts on some materials but not on other materials.
Physical devices which posses this force are called magnets.
Electromagnetism
is the part of science which deal with the relation between electricity and
magnetism.
MAGNET
Magnet is the substance having the
properties of attracting iron and its alloy.
GENERAL CLASSES OF MAGNET
Natural magnet
Lodestone (an iron compound) is a
natural magnet which was discovered centuries ago.
Artificial magnet
The magnets are made from various alloys
containing elements like copper, nickel, aluminum and cobalt.
These magnets are much, stronger than
the natural lodestone magnet.
Artificial magnet again classified as
i) Permanent magnet – The magnet which
retains the magnetic properties for a long period. It is available in different
shapes as (a) Bar magnets (b) U-shaped (c) Horse shoe magnets and (d) Compass
needle, etc.
ii) Electromagnet or temporary magnet –
The magnet which loses its properties as soon as the magnetizing force is
removed.
MAGNETIC MATERIALS
The most common magnetic materials are
iron, iron components, and alloys containing iron or steel.
Materials such as nickel and cobalt are
slightly magnetic. They are attracted by strong magnets. Compared with iron,
however, they are only weakly magnetic.
NONMAGNETIC MATERIALS
Materials which are not attracted by the
magnets are called nonmagnetic materials.
Examples are Copper, brass, aluminum,
silver, zinc and tin.
Nonmetals like wood, plastic, paper,
leather and rubber.
A nonmagnetic material does not stop
magnetic flux. Flux goes through nonmagnetic materials about as readily as it
goes through air.
PERMANENT
Many alloys of iron, especially those
contain more than 0.8% carbon become permanent magnet.
Tools such as screwdriver, pliers and
haw-saw blades, contain more than 0.8% carbon.
Most permanent magnets are made of alloys
such as Alnico) which can be highly magnetized.
Alnico magnets are composed of iron,
cobalt, nickel, aluminum and copper. Applications of permanent magnets are used
to make loud speakers, electric meters and motors.
TEMPORARY MAGNETS
Materials such as pure iron, ferrite and
silicon steel make temporary magnets. Applications of temporary magnets are
used in great quantities in motors, generators, transformers and
electromagnets.
PARAMAGNETIC SUBSTANCES
Para-magnetic substances are attracted by
magnets slightly. Its permeability is greater than unity. Examples:
Aluminum, copper sulphate and platinum
DIAMAGNETIC SUBSTANCES
Diamagnetic materials are repelled by
magnets. Its permeability is less than unity. Examples: gold, lead,
copper and antimony
FERROMAGNETIC SUBSTANCES
These materials are strongly attracted
by magnets. Its permeability is very much greater than unity ranging to several
thousands. Examples: Iron, Nickel and Cobalt
PERMEABILITY (µ)
It is the ratio between flux density to
flux intensity.
It is denoted by µ. µ = B / H. it has no unit, as it is a
ratio.
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