Ferromagnetic material used in transformers must have ______.

The correct option is: High permeability and Low Hysteresis loss.

To understand why this option is correct, let us analyze the role of ferromagnetic materials in transformers:

1. Magnetic Permeability:
Magnetic permeability is the measure of a material's ability to support the formation of a magnetic field within itself. In a transformer, the core's primary function is to couple the magnetic flux produced by the primary winding to the secondary winding with minimal leakage. A material with high permeability offers a low-reluctance (low magnetic resistance) path for the magnetic flux. This ensures that the maximum possible magnetic flux is confined within the core and transferred efficiently, thereby maximizing electromagnetic induction and reducing leakage flux.

2. Hysteresis Loss:
Hysteresis loss is the energy dissipated as heat due to the continuous reversal of magnetization of the transformer core when subjected to an alternating current (AC). The energy lost per cycle is proportional to the area of the hysteresis loop (B-H loop) of the material. To minimize energy waste and prevent the transformer from overheating, the core material must have a narrow hysteresis loop, which corresponds to low hysteresis loss. Materials like silicon steel are commonly chosen for this reason.

Therefore, to ensure high efficiency and minimal energy dissipation, a ferromagnetic material used in transformers must possess both high permeability and low hysteresis loss.