SI base unit referenced to the values of the fundamental constants, namely the Planck constant ("h"), the electron charge ("e"), the Boltzmann constant ("k"), and the Avogadro constant ("N"). This approach was approved in 2018, only after measurements of these constants were achieved with sufficient accuracy. SI base unit The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units and their physical quantities are the meter for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin
Electrical resistance and conductance Electrical resistance and conductance The electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is , and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S). The resistance of an object depends in large part on the material it is made of—objects made of electrical insulators like rubber tend to have very high resistance and low conductivity, while objects