Ferromagnetic Materials Uses Assignment Help

Electromagnetism - Ferromagnetic Materials Uses

Important properties of ferromagnetic materials are studied from their hysteresis curves. These3 properties help us in the proper selection of materials for various practical applications as detailed below. 
Permanent magnets permanent magnets are the materials which retain at room temperature their ferromagnetic properties for a long time. The applications as detailed below.
High retentively so that the magnet is strong,
High coercively so that the magnetization is not erased by stray magnetic fields temperature changes or mechanical damage due to rough handling etc. 
High permeability so that it can be magnetized easily.

Steel is preferred for making permanent magnets. Though retentively is steel is slightly smaller than that of soft iron yet it's coercively is much larger than that of soft iron. Other suitable materials for permanent magnets are cobalt steel, alnico (an alloy of iron aluminimum nickel cobalt and copper); diaconal and vocally. To make a permanent magnet we can hold a steel rod in the north south direction and hammer it repeatedly another way is to stroke the steel rod with one end of a bar magnet a very large number of items always in the same sense. 

A more efficient way to make a permanent magnet is to place a ferromagnetic rod in a solenoid and pass current through the solenoid the magnetic field to the solenoid magnetizes the rod. 

The core of electromagnets are made of ferromagnetic materials which have high permeability and low retentively soft iron is a suitable materials for this purpose when a soft iron rod is placed in a solenoid and current is passed through the solenoid magnetism of the solenoid is increased by a thousand fold when the solenoid current is switched off the magnetism is removed instantly as retentively of soft iron is very low. Electromagnets are used in electric bells. Loudspeakers and telephone diaphragms. Giant electromagnets are used in cranes to lift machinery etc.
Transformer cores. The materials used for making transformer cores chokes diaphragms of telephones etc. are subjected to as cycle of magnetization for a long period. Therefore low hysteresis loss is the first essential condition for such materials. The hysteresis curve of such materials must be narrow the energy dissipated and therefore heating of the material will be small. The material chosen must also have high resistivity to decrease energy losses due to eddy currents soft iron is most suitable for transformer cores. More effective alloys have also been developed for the purpose some of them are perm alloys mu metal and radio metal etc.
Some important terms used in magnetism 

Physical Quantity Symbol Nature Dimensions Units Remarks
Magnetic induction, magnetic flux density B Vector (MT-2 A-1) T 1T = 104 gauss
Magnetic intensity or magnetizing force H Vector [L-1 A] Am-1  
Intensity of magnetization I Vector [L-1 A] Am-1 I = M/V
Magnetic moment M Vector [L2A] Am2  
Magnetic permeability U Scalar [MLT-2A-2] Tm A-1  
Permeability of free space U0 Scalar [MLT-2A-2] Tm A-1 U0/4π=10-7
Relative magnetic permeability Ur Scalar N0 N0 μr-1 + ym

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