Magnetic flux area S is where "B" is the magnitude of the magnetic field (the magnetic flux density) having the unit of Wb/m (tesla), "S" is the area of the surface, and "θ" is the angle between the magnetic field lines and the normal (perpendicular) to S. For a varying magnetic field, we first consider the magnetic flux through an infinitesimal area element dS, where we may consider the field to be constant: A generic surface, S, can then be broken into infinitesimal elements and the total magnetic flux through the surface is then the surface integral From the definition of the
Energy density SI units) is where D is the electric displacement field and H is the magnetizing field. In the case of absence of magnetic fields, by exploting Fröhlich's relationships it is also possible to extend these equations to anisotropy and nonlinearity dielectrics, as well as to calculate the correlated Helmholtz free energy and entropy densities. Energy density Energy density is the amount of energy stored in a given system or region of space per unit volume. Colloquially it may also be used for energy per unit mass, though the accurate term for this is specific energy. Often only the "useful" or