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Electromagnets are made of soft iron because soft iron has
A
High retentivity and low coercive force
B
Low retentivity and high coercive force
C
High retentivity and high coercive force
D
Low retentivity and low coercive force
Detailed Solution
An electromagnet must become strongly magnetised when the current is on and lose its magnetism as soon as the current is switched off.
Low retentivity means very little magnetism remains when the magnetising field is removed.
Low coercivity means only a small reverse field is needed to demagnetise it, so it is easily magnetised and demagnetised; the hysteresis loop is narrow and the energy loss is small.
Soft iron has high permeability with low retentivity and low coercivity, so it is suitable. (Steel, with high coercivity, is used for permanent magnets.)
Hence soft iron is used because it has low retentivity and low coercive force.
Low retentivity means very little magnetism remains when the magnetising field is removed.
Low coercivity means only a small reverse field is needed to demagnetise it, so it is easily magnetised and demagnetised; the hysteresis loop is narrow and the energy loss is small.
Soft iron has high permeability with low retentivity and low coercivity, so it is suitable. (Steel, with high coercivity, is used for permanent magnets.)
Hence soft iron is used because it has low retentivity and low coercive force.