constant. where B and H are the magnetic fields M is magnetization is magnetic permeability is the permeability of vacuum (used in the SI system, but meaningless in Gaussian units); is the magnetic susceptibility The quantities and are both dimensionless, and they have the same numeric value. By contrast, the magnetic susceptibility and are both unitless, but has different numeric values in the two systems for the same material: Vector and scalar potentials The electric and magnetic fields can be written in terms of a vector potential A and a scalar potential φ: Electrical circuit where Q is the quantity of electricity I is the electric current V is the electric potential Φ is the magnetic flux R is the electrical resistance C is the capacitance L is the inductance Fundamental constants Electromagnetic unit names (For non-electromagnetic units, see Centimetre–gram–second system of units.) Note: The SI quantities and satisfy . The conversion factors are written both symbolically and numerically. The numerical conversion factors can be derived from the symbolic conversion factors by dimensional analysis. For example, the top row says , a relation which can be verified with dimensional analysis, by expanding and C in SI base units, and expanding Fr in Gaussian base units. It is surprising to think of measuring capacitance in centimetres. One useful example is that a centimetre of capacitance is the capacitance between a sphere of radius 1 cm in vacuum and infinity. Another surprising unit is measuring resistivity in units of seconds. A physical example is: Take a parallel-plate capacitor, which has a "leaky" dielectric with permittivity 1 but a finite resistivity. After charging it up, the capacitor will discharge itself over time, due to current leaking through the dielectric. If the resistivity of the dielectric is X seconds, the half-life of the discharge is ~0.05X seconds. This result is independent of the size, shape, and charge of the capacitor, and therefore this example illuminates the fundamental connection between resistivity and time units. Dimensionally equivalent units A number of the units defined by the table have different names but are in fact dimensionally equivalent – i.e., they have the same expression in terms of the base units cm, g, s. (This is analogous to the distinction in SI between becquerel and Hz, or between newton-metre and joule.) The different names help avoid ambiguities and misunderstandings as to what physical quantity is being measured. In