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Electromagnetism

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Ashish Bairwa

Electromagnetism is the property by which magnets attract pieces of iron. Magnets can be natural or artificial. Artificial magnets are made from iron, steel, or alloys and can be permanent or temporary. Permanent magnets retain magnetism for a long time, while temporary magnets only retain it while a magnetizing force is applied. A magnetic field is the area around a magnet's pole where its influence exists. Magnetic flux is the total number of field lines and flux density measures the concentration of flux per unit area. Magnetic field intensity is proportional to flux density. Permeability measures the degree to which a material concentrates magnetic field lines and can be expressed relative to permeability of free space.

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ELECTROMAGNETISM Some iron are having the property of attracting small pieces of iron eg:- magnetite (Fe3O4) Any body which shows the power of attracting pieces of iron is called magnet and the property by which this attraction take place is caaled magnetism. Magnets:- 1) Natural magnet (magnetite,stone) 2)Artificial magnet :- 1) Permanent 2) Temporary Artificial magnets are made artificially from iron,steel or alloy material. They can be prepared either by rubbing iron bars with a magnet or by passing an electric current through the wire,wound round on an iron piece. The 2nd method is more comman ,convenient and effective. The magnet prepared by this way are called electromagnets and the phenomena is caaled electromagnetism.
Permanent magnet :- the magnet prepared from hardness steel and certain alloys of nickel & cobatt,which retain the magnetism unaltered for long duration even after removal of magnetizing force are kniwn as permanent magnets. ALNECO is a widely used alloy for making permanent magnets Uses : Electrical instrument,earphone,loud speakers, telephone receivers,small dc motors etc. Temporary Magnets :- the magnet prepared from soft iron or nickel which retain magnetism as long as magnetizing force is applied are known as temporary magnets. They are easily and strongly magnetized but lose their strength as soon as the magnetizing force is removed. These magnets are of more importance as compared to permanents and have wide applications in the field of electeical generators,motors,relays etc.
Magnetic Fields :- the area around a magnetic pole of a magnet where its influence is there is called magnetic field. Line of force travel from the north to south pole. These are assumed to continuous through the magnet the point from which they have emerged. Thus each line of force from a closed path. Magnetic Flux () :- the total no of lines of force in the magnetic field is called the magnetic flux( Unit:-Weber Magnetic Flux density (B) :-the concentration of magnetic flux per unit area on a perpendicular plane is called flux density (B). B= Wb/m2 or tesla Magnetic field intensity (H) :- the mmt per unit length of flux path is called the magnetic field intensity (H).which is directly proportional to the magnetic flux density (B). H= mmt/length = NI/L & B×H Or B = µH where µ permeability
Permeability (µ) :- A magnetic material when placed in a magnetic field acquires magnetism due to induction. The measure of the degree to which the lines of force of the magnetizing field. The absolute permeability of the medium. The permeability of all non magnetic material including air is represented by µ µ= 4 10-7 H/M the absolute permeability µ of a medium or magnetic material can also be expressed in terms of its relative permeability µ5 and the permeability of free space or air (µ) µ= µ0 × µ5 µ0= relative permeability µ5= permeability of free space for diamagnetic material, µ< 1 for paramagnetic material,µ> 1 for fermagnetic material , µ>> 1000, 2000≤ µ ≤ 6000

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Electromagnetism

  • 1. ELECTROMAGNETISM Some iron are having the property of attracting small pieces of iron eg:- magnetite (Fe3O4) Any body which shows the power of attracting pieces of iron is called magnet and the property by which this attraction take place is caaled magnetism. Magnets:- 1) Natural magnet (magnetite,stone) 2)Artificial magnet :- 1) Permanent 2) Temporary Artificial magnets are made artificially from iron,steel or alloy material. They can be prepared either by rubbing iron bars with a magnet or by passing an electric current through the wire,wound round on an iron piece. The 2nd method is more comman ,convenient and effective. The magnet prepared by this way are called electromagnets and the phenomena is caaled electromagnetism.
  • 2. Permanent magnet :- the magnet prepared from hardness steel and certain alloys of nickel & cobatt,which retain the magnetism unaltered for long duration even after removal of magnetizing force are kniwn as permanent magnets. ALNECO is a widely used alloy for making permanent magnets Uses : Electrical instrument,earphone,loud speakers, telephone receivers,small dc motors etc. Temporary Magnets :- the magnet prepared from soft iron or nickel which retain magnetism as long as magnetizing force is applied are known as temporary magnets. They are easily and strongly magnetized but lose their strength as soon as the magnetizing force is removed. These magnets are of more importance as compared to permanents and have wide applications in the field of electeical generators,motors,relays etc.
  • 3. Magnetic Fields :- the area around a magnetic pole of a magnet where its influence is there is called magnetic field. Line of force travel from the north to south pole. These are assumed to continuous through the magnet the point from which they have emerged. Thus each line of force from a closed path. Magnetic Flux () :- the total no of lines of force in the magnetic field is called the magnetic flux( Unit:-Weber Magnetic Flux density (B) :-the concentration of magnetic flux per unit area on a perpendicular plane is called flux density (B). B= Wb/m2 or tesla Magnetic field intensity (H) :- the mmt per unit length of flux path is called the magnetic field intensity (H).which is directly proportional to the magnetic flux density (B). H= mmt/length = NI/L & B×H Or B = µH where µ permeability
  • 4. Permeability (µ) :- A magnetic material when placed in a magnetic field acquires magnetism due to induction. The measure of the degree to which the lines of force of the magnetizing field. The absolute permeability of the medium. The permeability of all non magnetic material including air is represented by µ µ= 4 10-7 H/M the absolute permeability µ of a medium or magnetic material can also be expressed in terms of its relative permeability µ5 and the permeability of free space or air (µ) µ= µ0 × µ5 µ0= relative permeability µ5= permeability of free space for diamagnetic material, µ< 1 for paramagnetic material,µ> 1 for fermagnetic material , µ>> 1000, 2000≤ µ ≤ 6000