Assertion: Soft iron is used as transformer core.
Reason: Soft iron has narrow hysteresis loop.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If assertion and reason both are false.

Answer

A

Explanation

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 hysteresis 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 (ferromagnetic substance) has high permeability, high retentivity, low coercivity and low hysteresis loss.