Electromagnets
Electromagnets are made of soft iron because area of hysteresis loop for soft iron is small . Therefore , energy loss is small for a cycle of magnetisation and demagnetisation .
( Permanent magnets are made by the materials such as steel , for which residual magnetism as well as coercivity should be high . Electromagnets are made by the materials such as soft iron for which residual magnetism is high , coercivity is low and hysteresis loss is low ).
Important Points
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Magnetic length = 5 / 6 * geometric length of magnet . �
About 90 % of magnetic moment is due to spin motion of electrons and
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remaining 10 % of magnetic moment is due to the orbital motion of electrons . �
When a magnet having magnetic moment M is cut into two equal parts�
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( i ) Parallel to its length |
M ’ = m / 2 * l = M / 2
( ii ) Perpendicular to its length M ’ = m * l / 2 = M / 2
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When a magnet of length I , pole strength m and of magnetic moment M is turned into a semi-circular arc then it new magnetic moment�
M ’ = m * 2R = m * 2 * 1 / π ( πR = I ) = 2M / π ( M = m * l )