A non-permanent magnet, also known as a temporary magnet, is a material that exhibits magnetic properties only when subjected to an external magnetic field. Unlike permanent magnets, which retain their magnetism even after the external field is removed, non-permanent magnets lose their magnetism once the external field is gone. This crucial difference stems from the fundamental nature of their magnetic domains.
How Non-Permanent Magnets Work: The Role of Magnetic Domains
All materials are composed of tiny regions called magnetic domains. These domains are essentially groups of atoms whose magnetic moments are aligned, creating a small magnetic field. In a permanent magnet, these domains are spontaneously aligned, resulting in a strong overall magnetic field. However, in a non-permanent magnet, the domains are randomly oriented. When an external magnetic field is applied, it aligns these domains temporarily, inducing a net magnetic field in the material. This is why the material behaves like a magnet only while under the influence of the external field.
The Most Common Type: Electromagnets
The most prevalent example of a non-permanent magnet is an electromagnet. These are created by passing an electric current through a coil of wire wrapped around a ferromagnetic core (like iron). The electric current generates a magnetic field that aligns the domains in the core, creating a powerful temporary magnet. Crucially, when the current is switched off, the magnetic field collapses, and the domains return to their random orientation, resulting in the loss of magnetism.
Strengths and Applications of Electromagnets
Electromagnets offer several advantages over permanent magnets:
- Controllability: The magnetic field's strength can be easily controlled by adjusting the electric current. A higher current leads to a stronger magnetic field.
- On/Off Switchability: The magnetic field can be turned on and off instantly by simply controlling the flow of electricity.
- Variable Strength: The magnetic field strength can be finely adjusted to suit specific applications.
These features make electromagnets incredibly versatile, leading to their widespread use in numerous applications including:
- Electric Motors and Generators: Electromagnets are essential components, converting electrical energy into mechanical energy and vice-versa.
- Magnetic Resonance Imaging (MRI) Machines: Powerful electromagnets are used to generate strong magnetic fields for medical imaging.
- Magnetic Levitation (Maglev) Trains: Electromagnets enable these trains to levitate above the tracks, enabling high-speed travel.
- Lifting Heavy Objects: Electromagnetic cranes use powerful electromagnets to lift and move ferrous materials efficiently.
- Speakers and Headphones: Electromagnets convert electrical signals into sound waves.
Other Materials Exhibiting Temporary Magnetism
While electromagnets are the most prominent example, other materials can also display temporary magnetic properties under specific conditions. Certain alloys and paramagnetic materials can exhibit weak temporary magnetism when exposed to a strong external magnetic field. However, the magnetism induced in these materials is significantly weaker than that produced by an electromagnet.
Distinguishing between Permanent and Non-Permanent Magnets
The key difference lies in their ability to retain magnetism after the external field is removed. Permanent magnets retain their magnetization due to the strong alignment of their magnetic domains, while non-permanent magnets lose their magnetization due to the random orientation of their domains when the external field is absent.
This detailed explanation helps solidify the understanding of non-permanent magnets and their crucial role in various technological applications. Understanding this difference between permanent and temporary magnets is fundamental to comprehending the principles of magnetism and electromagnetism.
