Temporary magnets are materials that exhibit magnetic properties only when exposed to an external magnetic field or when an electric current flows through them. Their ability to switch magnetism on and off makes them distinct from other magnetic substances. This characteristic allows for controlled magnetic effects in various applications.
The Science Behind Temporary Magnetism
The behavior of temporary magnets stems from tiny magnetic regions within their atomic structure, known as magnetic domains. In materials like iron or nickel, each atom acts like a miniature magnet, and groups of these atoms align to form these domains. Without an external magnetic field, these domains are oriented randomly, canceling out each other’s magnetic effects, so the material does not appear magnetic.
When an external magnetic field is introduced, it exerts a force on these domains. The domains within the material begin to rotate and align with the direction of the external field. This alignment creates a net magnetic field within the material, causing it to become temporarily magnetized.
Once the external magnetic field is removed, the aligned domains quickly lose their ordered arrangement. Thermal energy and internal atomic structures cause the domains to return to their original, random orientations. This disorganization results in the material losing its induced magnetic properties. The ease with which domains align and disalign is a defining feature of temporary magnetic materials.
Where You Find Temporary Magnets
Temporary magnets are composed of materials like soft iron, nickel, and certain alloys, which allow their magnetic domains to align and disalign easily. A common application is in electromagnets, which use an electric current to create a magnetic field. When electricity flows through a coil of wire wrapped around a soft iron core, the iron becomes a powerful magnet.
Electromagnets are used extensively in industrial settings, such as in scrapyards where large electromagnets lift and move heavy metal objects. When the current is switched off, the metal is released. Everyday devices also incorporate temporary magnets, including electric doorbells, which use an electromagnet to strike a chime, and magnetic locks, which secure doors when an electric current magnetizes a component.
Even a simple paperclip can demonstrate temporary magnetism. If a permanent magnet touches a paperclip, the paperclip temporarily becomes magnetized and can pick up other small metal objects. As soon as the permanent magnet is removed, the paperclip loses its magnetism because its domains quickly return to a disordered state.
Temporary Versus Permanent Magnets
The distinction between temporary and permanent magnets lies in their ability to retain magnetism once an external magnetic field is removed. Temporary magnets only exhibit magnetism while under the influence of an external field or an electric current. Their magnetic domains readily return to a random orientation when the external influence ceases.
Permanent magnets, conversely, maintain their magnetic properties even after the external field that magnetized them is removed. This enduring magnetism is because their magnetic domains are difficult to disalign once oriented. Materials like steel or alnico alloys are often used for permanent magnets because their domains remain locked in alignment.
The stability of magnetic domains dictates the uses of each type of magnet. Temporary magnets are valuable in applications requiring controllable magnetic forces, such as in relays, circuit breakers, and magnetic recording heads, where magnetism needs to be switched on and off rapidly. Permanent magnets are used where a constant magnetic field is desired, like in refrigerator magnets, compasses, and electric motors, providing continuous magnetic attraction without external power.