Steel is preferred to soft iron for making permanent magnets primarily due to its magnetic properties, particularly its coercivity. Coercivity is a measure of the resistance of a ferromagnetic material to becoming demagnetized. A higher coercivity means that the material can maintain its magnetization in the presence of external magnetic fields or physical disturbances. Among the given options, the correct answer is: Option C: Steel has more coercivity than soft iron Here's a more detailed explanation: Coercivity is crucial for permanent magnets because it determines the ability of the material to retain its magnetic properties over time. Soft iron has a low coercivity, making it easy to magnetize and demagnetize. This property makes soft iron suitable for temporary magnets or electromagnets, where a quick magnetic response is needed. On the other hand, steel has a much higher coercivity compared to soft iron. This higher coercivity allows steel to retain its magnetization even after the external magnetic field is removed. Hence, steel is more suitable for making permanent magnets, as it can maintain its magnetic state for a long period of time without significant loss of magnetic strength. The concept of coercivity can be mathematically represented by the hysteresis loop of a material. The wider the loop, the higher the coercivity. For a permanent magnet, the area within the hysteresis loop is also significant as it indicates the energy stored in the magnet. In mathematical terms, coercivity Hc can be understood from the hysteresis curve of the material. The point Hc is where the magnetization M or B, which represents the magnetic flux density, returns to zero when an external magnetic field is applied in the reverse direction:
Hc=‌ Coercivity of the material ‌ Therefore, the key property that makes steel more suitable than soft iron for making permanent magnets is its higher coercivity.