How do some magnets have the ability to turn on and off?


Why don’t all magnets have this ability? Is it based on the material? If a magnet is turned off, is it that the material is demagnetized somehow and then magnetized again?

In: Engineering

Electromagnets can be turned on and off by adding current/electricity. Natural magnets cannot be turned on and off.


You are thinking of electromagnets that can be turned on and off. Electromagnets are a non magnetic material like copper that becomes magnetic when an electric current is applied to it.

Some if not most (modern) welding clamp magnets have a switch that “turns them of” seemingly without power like most electromagnets require, all that is though is the magnet, which is an “always on” rare earth magnet, is changing physical position a bit inside so its magnetic field has little to no effect through the casing it is in, its a really clever system that works amazing.

In classical physics, Maxwell’s equations govern how electricity and magnetism work.

Under these laws there are electric fields and magnetic fields and the two interact with each other. The electric field is easy to understand(likes repel and opposite attract). Magnetism is more complex and results from the movement of electric fields between each other. For example say you have a test electron near a neutral currentless wire, nothing will happen. But when the wire has current electric charges are moving past the test electron and the electron will feel a force even though the wire is still neutrally charged. This force is magnetism and its perpendicular to direction of motion. Therefore any conductive material with a current will create a magnetic field.

To get more advanced magnetism is a manifestation of special relativity on the electric force. In special relativity relative motion causes length contraction. Therefore electric charges will “feel” different forces as other charges expand or contract depending on their speed.