Magnetic moment and external fields is not part of this internal energy. The unit for magnetic moment in terms of the International System of Units (SI) base units is A⋅m, where A is the ampere (the SI unit of current) and m is the meter (the SI unit of distance). This has equivalents in other units used in SI including: where N is the newton (the SI unit of force), T is the tesla (the SI unit of magnetic flux density), and J is the joule (the SI unit of energy). In the CGS system, there are several different sets of electromagnetism
Spectral flux density flux density will suffice. Spectral flux density In spectroscopy, spectral flux density is the quantity that describes the rate at which energy is transferred by electromagnetic radiation through a real or virtual surface, per unit surface area and per unit wavelength. It is a radiometric measure, as distinct from measures that characterize light in terms of the brightness to the eye, or photons. In SI units it is measured in W m, although it can be more practical to use W m nm (1 W m nm = 1 GW m = 1 W mm) or W m μm (1