Question

Hysteresis loop for two magnetic material $A$ and $B$ are given below:


These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use

• A. $B$ for electromagnets and transformers
• B. $A$ for transformers and $B$ for electric generators
• C. $A$ for electric generators and transformers
• D. $A$ for electromagnets and $B$ for electric generators

Answer 1

The correct option is A $B$ for electromagnets and transformers

• For the transformer core and electromagnet core we need temporary magnets and for electric generators we need permanent magnets.

• The desired properties of material suitable for making temporary magnets are low retentivity and coercivity and less hysteresis loss.

• For above qualities , the hysteresis curve of substance should be long and narrow.

• low retentivity ensures that material gets easily demagnetised when magnetizing field is removed , low coercivity ensures that material can be easily magnetised in opposite direction and narrow hysteresis loop ensures small area of hysteresis of curve and hence less hysteresis loss during cycle of magnetisation and demagnetisation.

• materials having high retentivity and high coercivity are suitable for making permanent magnets

• high retentivity ensures that the material retains its magnetic property strongly even in absence of external magnetising field and high coercivity ensures that the material doesn’t get demagnetised in presence of opposite external field.

• Thus, graph A represents hysteresis loop for permanent magnets. Graph B represents material suitable for temporary magnets.

Hence, correct option is $\left(d\right)$