The hysteresis loss in a D.C. machine least depends on

The other options are all factors that affect the hysteresis loss.

• Frequency of magnetic reversals: The higher the frequency of magnetic reversals, the greater the hysteresis loss. This is because the magnetic domains have to move more often to follow the changing field.
• Maximum value of flux density: The higher the maximum value of flux density, the greater the hysteresis loss. This is because the magnetic domains have to be further displaced to follow the changing field.
• Volume and grade of iron: The larger the volume of iron and the higher the grade of iron, the greater the hysteresis loss. This is because the magnetic domains have more space to move and are more easily displaced in higher-grade iron.