If Magnet Keeps Doing External Work, Will Its Magnetism Become Weaker?
The problem itself is actually a misunderstanding of magnets.
Magnets can do work, but they do not consume their own magnetism in the process of doing work. Magnets look magical, but they are actually not mysterious. The principle is very similar to that of springs. The magnetism of magnets is just a channel for storing and releasing energy.
For example, put a thing into a magnetic field, the energy of the thing is not provided by the magnetic field, but by the force that puts that thing in the magnetic field.
The same goes for springs, which store energy when compressed and release energy when released.
So how does the magnetism of a magnet come about?
The essence of magnetism is in the microscopic world. There are many microscopic units (magnetic domains) inside the magnet. The magnetic fields of these microscopic units are aligned in the same direction, which produces magnetism.
As long as the magnetic fields of the tiny cells inside the magnet don’t get chaotic, the magnetism will never go away.
It can be seen that magnetism is an inherent property of magnets, which always exists, regardless of whether it does work or not. A magnet loses its magnetic field, not because of work, but only because of disordered changes in the microscopic magnetic domains inside the magnet.
The magnetism of a magnet is not the same as an electromagnetic field, which requires current to maintain the magnetic field, so as long as the magnetic field does not output energy (doing work), the electrical energy will not be lost (perfectly).
If there is no energy input, the magnet will not do external work. For example, for a pair of repulsive magnets, an external force must push one of the magnets against the repulsive force before it can do work. Similarly, the magnets that attract each other must have an external force to separate the two magnets, and after they are released again, work can be done to make the two magnets attract together.
For example, in the picture above, an iron wrench is attracted by a magnet. In fact, the wrench was artificially placed at a certain distance from the magnet. In this artificial process, the wrench has actually acquired the potential energy of the magnetic field, and the process of attracting the wrench is the potential energy. It is released only, it has no effect on the magnetism of the magnet.
Our common motor also uses the magnetic field potential energy to provide kinetic energy, and consumes the energy passing through the magnetic field, not the magnetic field itself.
Therefore, for a magnet that looks very interesting, whether the magnetism disappears or not has nothing to do with the work. The magnetism is the intrinsic property of the magnet, just as the elasticity is the intrinsic property of the spring, and the elasticity of the spring has nothing to do with the work.