A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but reason is not the correct explanation of the assertion.
C) If assertion is true but reason is false.
D) If the assertion and reason both are false.
E) If assertion is false but reason is true.
Correct Answer: A
Solution :
The core of a transformer undergoes cycles of magnetisation again and again. During each cycle of magnetisation, energy numerically equal to the area of the hysteresis loop is spent per unit volume of the core. Therefore, for high efficiency of transformer, the energy loss will be lesser if the hystersis loop is of lesser area, i.e. narrow. That?s why the soft iron is used as core, which has narrow hysteresis loop (or area of \[B-H\] curve is very small). Also soft iron (ferromegnetic substance) has high permeability, high retentivity, low coercivity and low hystersis loss.
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