siemens

The siemens (S) is a SI unit of electrical conductance, the reciprocal of electrical resistance, and the unit is the reciprocal of the SI unit of resistance, the ohm. The term mho, which is ohm spelled backward, is used by some instead of siemens. Relationships:

C = 1/R = I/V

• C - conductance in siemens.
• R - resistance in ohms.
• I - current in amperes (amps).
• V - voltage in volts.

The siemens is a derived SI unit from the base units kg^-1m^-2s³A² (i.e., kilograms, meters, seconds, and amperes).

Two other quantifications, electrical resistivity and conductivity are measures of a material's electrical resistance and conductance characteristics, i.e., how much of a given material produces a certain resistance or conductance. Resistivity is commonly given as ohm-meters (Ω-m), a meter-cube of the material with a resistivity of N ohm-meters has a resistance of N ohms. A material's conductivity is the reciprocal of its resistivity, commonly given as siemens per meter (S/m). (Note that the "distance" indicated by meter, in both resistivity and conductivity, actually indicates the material's cross section divided by its length.)