where E o p e n c i r c u i t is the conservative electrostatic field created by the charge separation associated with the emf, d ℓ ℓ is an element of the path from terminal N to terminal P, ' ⋅ ⋅ ' denotes the vector dot product, and V is the electric scalar potential. This emf is the work done on a unit charge by the source's nonelectrostatic field E ′ when the charge moves from N to P.