The desirable properties for making permanent magnets are

Options

A. high retentivity and high coercive force
B. high retentivity and low coercive force
C. low retentivity and high coercive force
D. low retentivity and low coercive force.

Answer

To determine the desirable properties for making permanent magnets, we need to understand the concepts of retentivity and coercivity, which are crucial in the context of magnetic materials. Here’s a step-by-step solution:

### Step 1: Understand the Concepts
- **Retentivity**: This is the ability of a magnetic material to retain its magnetization after the external magnetic field is removed. A high retentivity means the material can hold onto its magnetic properties for a long time.
- **Coercivity**: This refers to the resistance of a magnetic material to changes in magnetization. High coercivity means that a material requires a strong external magnetic field to demagnetize it.

### Step 2: Analyze the Hysteresis Loop
- The hysteresis loop represents the relationship between magnetic field strength (H) and magnetic flux density (B).
- The area of the loop indicates energy loss during magnetization and demagnetization cycles, which is important for understanding the efficiency of a permanent magnet.

### Step 3: Identify Desirable Properties
- For a material to be a good permanent magnet, it should have:
- **High Retentivity**: To ensure that the magnet retains its magnetization over time.
- **High Coercivity**: To ensure that the magnet does not easily lose its magnetization when exposed to external magnetic fields.

### Step 4: Conclusion
- Therefore, the desirable properties for making permanent magnets are high retentivity and high coercivity. This ensures that the magnet can maintain its magnetic properties for a long duration and resist demagnetization.

### Final Answer
The desirable properties for making permanent magnets are:
- High Retentivity
- High Coercivity