Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 145

Similar to the electric charge distribution, the magnetic charge distribution can be assumed in a volume of the body. The magnetic charge density is expressed as ρ_m. The magnetic charge creates a magnetic flux Ψ_m. Similar to the case of the electric charge, the elemental magnetic charge in the volume dv is ρ_mdv, and the elemental magnetic flux coming out of the surface is where is the magnetic flux density as ds is the elemental surface of the enclosed volume v. It is also called the magnetic displacement vector. The Gauss’s law for the magnetic charge and magnetic flux can be written in the integral form as follows:

(4.1.4)

Figure 4.1 The unit vector is in the direction normal to the surface.

Again, by using Gauss’s vector integral identity, the above expression is written below in the differential form:

(4.1.5)

However, the magnetic charges are not found in nature, i.e. ρ_m = 0. Therefore,

(4.1.6)

The amount of charge, or current, is an absolute quantity. It does not dependent on the material medium. Thus, the corresponding flux or the flux density is also not dependent on the surrounding medium. In brief, the charge and current create the electric and magnetic flux field, i.e. the flux densities ; and these are not influenced by a material medium.

Experiments demonstrate that the electrically charged body, or a current‐carrying conductor, interacts with other charged body, or another current‐carrying conductor. Such interaction, i.e. the mutual force, is influenced by the medium surrounding these bodies. Therefore, medium‐independent flux densities cannot explain the interaction between two charged bodies or current‐carrying conductors. The interactions between the charges and current‐carrying conductors take place through the force fields, expressed by the electric field intensity and magnetic field intensity . The field intensities are also responsible for the electromagnetic (EM)‐power transportation through a medium. However, the field intensities are influenced by the electrical and magnetic properties of a medium.