# Units

Two sets of units may be used to represent the magnetic permeability: Teslas times meters per Ampere (T $$\! \cdot \!$$ m/A), and Henrys per meter (H/m):

(21)$\frac{H}{m} = \frac{T \cdot m}{A}$

The magnetic field intensity $${\bf H}$$ is frequently given in Amperes per meter (A/m), whereas the magnetic flux density is given in Teslas (T). Therefore, the first choice in units is defined by the magnetic constitutive relationship. Henrys are used to represent a unit of magnetic inductance. Therefore, the magnetic permeability also characterizes the magnetic inductance per unit length of a material.

More commonly, the magnetic properties of rocks are represented using the magnetic susceptibility $$\chi$$. Magnetic susceptibility represents the proportion of total magnetic flux density attributed to induced magnetization. A physical description of the magnetic susceptibility is discussed in Magnetism in Rocks. Magnetic susceptibility is related to the magnetic permeability by the following equation:

(22)$\mu = \mu_0 \big [ 1 + \chi \, \big ]$

where $$\mu_0 = 4\pi \times 10^{-7}$$ H/m is the permeability of free-space. The correct SI units for magnetic susceptibility are (A/m)/(A/m). However, it is commonly expressed as a unitless quantity. Magnetic susceptibilities are occasionally given in CGS units. The conversion between SI and CGS units is given by:

(23)$\chi^{(SI)} = 4\pi \chi^{(CGS)}$