The key difference between permanent and temporary magnets lies in their ability to retain magnetism after the magnetizing force is removed: permanent magnets retain their magnetism indefinitely, while temporary magnets lose most of theirs.
Permanent Magnets
- Definition: Permanent magnets are materials that, once magnetized, maintain their magnetic field even without an external magnetic field or electric current.
- Material: Typically made from ferromagnetic materials like iron, nickel, cobalt, and alloys such as alnico (aluminum, nickel, and cobalt) and ferrite.
- Magnetization: They require a strong magnetic field to become magnetized initially.
- Retentivity: High retentivity, meaning they strongly resist demagnetization. This is why they remain magnetic for a very long time.
- Examples: Refrigerator magnets, compass needles, magnets used in electric motors and generators.
Temporary Magnets
- Definition: Temporary magnets are materials that exhibit magnetism only when under the influence of an external magnetic field or electric current. Once the external force is removed, their magnetism largely disappears.
- Material: Typically made from soft iron.
- Magnetization: They are easily magnetized by a relatively weak magnetic field.
- Retentivity: Low retentivity, meaning they easily lose their magnetism.
- Examples: Electromagnets used in cranes, the core of transformers, temporary magnetic holding devices.
Summary Table
| Feature | Permanent Magnet | Temporary Magnet |
|---|---|---|
| Magnetism | Retains magnetism indefinitely | Loses most magnetism when force is removed |
| Material | Ferromagnetic materials (e.g., alnico) | Soft iron |
| Magnetization | Requires strong magnetic field | Easily magnetized by weak field |
| Retentivity | High | Low |
| Examples | Refrigerator magnets, compasses | Electromagnet cores |
