potential difference (pd) The energy required to transfer one coulomb of charge between two points. For two arbitrary points a and b the potential difference V_ab is given by,

V_ab=V_b-V_a= W_ab/Q [volts]

where W_ab is the energy required to transfer Q coulomb. The values of V_b and V_a are unique for the point a and b ( see conservative field). The SI unit of potential difference is volt.