Materials used for making permanent magnet must have ______ retentivity and ______ coercivity.

Explanation:

Materials Used for Making Permanent Magnet

Definition: Permanent magnets are materials that maintain a persistent magnetic field without the need for an external power source. They are made from ferromagnetic materials, which have high magnetic permeability and are capable of being magnetized. The performance of a permanent magnet is determined by its magnetic properties, particularly its retentivity and coercivity.

Key Properties:

• Retentivity: Retentivity, also known as magnetic remanence, is the ability of a material to retain a certain amount of residual magnetism when the external magnetic field is removed. High retentivity is crucial for permanent magnets because it ensures that they remain magnetized over time without significant loss of magnetic strength.
• Coercivity: Coercivity is the resistance of a ferromagnetic material to becoming demagnetized. It is the measure of the intensity of the applied magnetic field required to reduce the magnetization of a material to zero after it has been magnetized. High coercivity is important for permanent magnets to prevent them from losing their magnetization due to external magnetic fields or mechanical stresses.

Correct Option Analysis:

The correct option is:

Option 1: high retentivity, high coercivity

This option is correct because materials used for making permanent magnets must have both high retentivity and high coercivity. High retentivity ensures that the magnet remains magnetized over time, while high coercivity ensures that the magnet resists demagnetization from external influences. These properties are essential for the effective and long-lasting performance of permanent magnets.

Additional Information:

To further understand the analysis, let’s evaluate the other options:

Option 2: high retentivity, low coercivity

This option is incorrect because while high retentivity is important for maintaining magnetization, low coercivity would make the magnet susceptible to demagnetization by external magnetic fields or mechanical stresses. Therefore, both high retentivity and high coercivity are necessary for a material to be suitable for making permanent magnets.

Option 3: low retentivity, high coercivity

This option is incorrect because low retentivity means the material cannot maintain a strong residual magnetic field when the external magnetizing force is removed. Despite having high coercivity, the material would not be effective as a permanent magnet due to its inability to retain significant magnetization.

Option 4: low retentivity, low coercivity

This option is incorrect because low retentivity would result in weak residual magnetism, and low coercivity would make the material easily demagnetized. Both properties are undesirable for permanent magnets, which require strong and stable magnetic fields over time.

Conclusion:

Understanding the magnetic properties of materials is crucial for selecting suitable candidates for permanent magnets. High retentivity ensures that the magnet retains its magnetic field, while high coercivity ensures that the magnet resists demagnetization. Therefore, the correct option for materials used in making permanent magnets is high retentivity and high coercivity. This combination of properties ensures that the magnets are both strong and stable over time, making them suitable for various applications in industrial and consumer products.