What are the uses of studying hysteresis curve of substance ?

Explanation

### Step-by-Step Solution:

1. **Understanding Hysteresis Curve**: The hysteresis curve represents the relationship between the magnetization (D) of a material and the applied magnetic field strength (H). It shows how a material responds to changes in the magnetic field, indicating properties such as retentivity and coercivity.

2. **Identifying Key Properties**: The hysteresis curve provides important information about two key properties of magnetic materials:
- **Retentivity**: The ability of a material to retain magnetization after the external magnetic field is removed.
- **Coercivity**: The resistance of a magnetic material to changes in magnetization, particularly the ability to withstand demagnetization.

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