To attain the highest flux density for a low value of magnetizing flux, the best magnetic material of the following is
A. permalloy.
B. soft iron.
C. brass.
D. aluminum.
The correct answer and explanation is:
The correct answer is B. soft iron.
Soft iron is widely recognized as one of the best magnetic materials for attaining a high magnetic flux density with a low magnetizing force (or magnetizing flux). This is because soft iron has very high magnetic permeability, meaning it allows magnetic lines of force to pass through it very easily. The higher the permeability, the less magnetizing force is needed to achieve a certain level of magnetic flux density.
Magnetic flux density (B) depends on the magnetizing force (H) and the material’s permeability (μ). The relationship can be expressed as B = μH. A material with high permeability requires a smaller H (magnetizing force) to produce a large B (flux density).
Soft iron’s structure allows its magnetic domains to align quickly and easily in response to an external magnetic field, creating strong magnetization. It has low coercivity and low hysteresis loss, which means it can magnetize and demagnetize with minimal energy loss and without retaining significant residual magnetism. These properties make it ideal for applications like transformers, inductors, and electromagnets, where efficient magnetization and demagnetization are crucial.
By contrast, permalloy is a nickel-iron alloy with very high permeability but is often used in applications where extremely low coercivity is needed, such as in magnetic shielding or sensitive magnetic sensors. While it is good, soft iron generally produces a higher flux density for a given magnetizing force due to its specific magnetic characteristics.
Brass and aluminum are non-magnetic materials and do not contribute significantly to magnetic flux density. They have very low permeability close to that of free space, so they cannot attain high flux densities under low magnetizing flux.
In summary, soft iron is the best choice among the options to achieve the highest flux density with the lowest magnetizing flux because of its high permeability, low coercivity, and efficient domain alignment.