Resistance and conductance

The unit of electric resistance is the ohm( ), where one ohm is one volt per ampere. It is defined as the resistance between two points in a conductor when a constant electric potential of one volt applied at the two points produces a current flow of one ampere in the conductor. Thus,

whereV is the potential difference across the two points, in volts, and I is the current flowing between the two points, in amperes. The reciprocal of resistance is called conductance and is measured in siemens (S). Thus

where R is the resistance in ohms.