Question

Which of the following is used to minimize hysteresis loss?
${\text{A}}{\text{.}}$ Soft iron core
${\text{B}}{\text{.}}$ Soft iron core with 4 % Si
${\text{C}}{\text{.}}$ Cobalt core
${\text{D}}{\text{.}}$ Ferrite core
${\text{E}}{\text{.}}$ Radiomental

Answer 1

Hint- Here, we will proceed by defining magnetic hysteresis. Then, we will discuss in an elaborative sense the existence of hysteresis losses. Finally, we will write down the basic method to minimize these losses.

Step-By-Step answer:
The magnetization phenomenon which lags behind the producing field is called magnetic hysteresis. Every Ferromagnetic material used in transformer cores has phenomena of hysteresis.
There are domains in the internal structure of ferromagnetic materials such as iron. Domain scale can range from 1 micrometre to 1 millimetre. Such domains consist of a variety of magnetic dipoles within the domain that are parallel to each other. There are unpaired spinning electrons in every atom in ferromagnetic material that act as magnetic dipoles. Every atom has a non-zero magnetic moment associated with it. Net magnetization in a ferromagnetic material would be zero because of the spontaneous alignment of domains with no applied magnetic field.
Once an external magnetic field is applied, all these domains align in the magnetic field direction in such a way that it gives rise to a net magnetic field. Now the external field is gone, most of the domains are again randomly aligned after removal of the external field. But some of the domains preserve their orientation because of the crystal deficiencies (dislocations) that result in permanent magnetization. When the strength of the applied magnetic field regularly changes after some period, the hysteresis loop is traced once. To make the field inside the material zero an external magnetic field should be applied opposite to the direction of iron magnetization.
In order to achieve magnetization and demagnetization of various domains, some amount of extra work is done which is known as hysteresis loss.
Most low frequency power transformers and inductors use laminated cores made of stacks of thin sheets of silicon steel to minimize the eddy current losses. Materials with high permeability and low coercion are used for providing a core with low hysteresis loss and low leakage of flux. Silicon steel is the alloy with low coercion and high magnetic permeability suitable for the transformer core. Silicon steel is simply soft iron with 4 % Si.
Therefore, option B is correct.

Note- The extent up to which a material gets magnetized depends upon the permeability of the material (${\mu _{\text{r}}}$) and the applied magnetic field strength (H) i.e., ${\text{M}} = \left( {{\mu _{\text{r}}} - 1} \right){\text{H}}$ where M is the extent of the magnetization of the material. As the strength or intensity of the applied magnetic field increases, the magnetization also increases till it reaches saturation.