Hello community!
I want to ask a question that might be pretty silly to some of you. In the magnetic induction equation, when we consider the external magnetic field, do we have to consider the magnetization of the medium too?
Let's suppose we have a liquid film at rest with an external transversal magnetic flux B0. The liquid will be magnetized, creating a magnetic flux B1 that will be proportional to the external one.
Let's assume that the liquid film starts to move. The relative motion of the liquid, which is assumed to be a ferromagnetic material, with respect to the external magnetic field will engender an induced current density field in the medium. In turn, the current will generate its own magnetic field. The creation of this secondary induced magnetic field b is generally described by the magnetic induction equation. In this equation, the unknown function B is assumed to be given by the sum of the external field B0 and the induced one b.
In the literature, people are not considering the magnetization field B1 in the magnetic induction equation. In my opinion, this is not a generally valid assumption, because it does not account for the penetration of the external magnetic field in the medium due to the magnetization. Moreover, for some materials, the magnetic flux field inside the medium would be even higher than the external one.
From a more physical perspective, the velocity field inside the liquid enters in contact with the magnetic field inside the medium, the one given by the external one multiplied by a constant factor given by the permeability of the material.
Thomas Breuer
thank you for your reply. When I mentioned current, I meant the actual electric current density in the medium.The point is that the current, in a fairly good approximation, will be given by the cross product of the velocity vector v with the magnetic flux vector B. If we assume that the velocity field and the magnetic field are constant and uniform, the current density field will also be constant and uniform. So, there will not be a compensation of positive and negative currents, leading to a neutral macroscopic condition.
Thomas Breuer
The liquid is not an ionized material. It is assumed to be molten metal. The current is generated in accordance with the Maxwell–Faraday equation, even though the magnetic flux field is stationary the ferromagnetic medium is moving with respect to it.The point which is puzzling me is that in the steady-state conditions the magnetic flux field inside the liquid would be proportional to the external one thanks to the appearance of a magnetization field, with a proportionality constant that depends on both the material and geometry properties of the medium. Now if we consider an unsteady condition, where the liquid is moving, there will be also an induced magnetic flux field b. This field is generally calculated with the magnetic diffusion equation, assuming the magnetic flux is given by the sum of the external field and the induced one. I do not understand because we do not consider the magnetic field inside the liquid due to the magnetization.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Condensed Matter Physics
- Soft Matter
- Liquids