Page 176 of MCAT Physics and Math Review 2026-2027 mentions "Electric potential is defined as the ratio of the magnitude of a charges electric potential energy to the magnitude of the charge itself", expressing that relationship as "V = U/q"
The book later states the following on page 177: "If Va and Vb are the electric potentials at points a and b respectively, then the potential difference between them, known as voltage, is Vb-Va", expressing that relationship as "∆V = Wab / q"
Earlier on page 175, it states "Electric potential energy is the work necessary to move a test charge from infinity to a point in space in an electric field surrounding a source charge", expressing that relationship as "∆U = Wab"
It follows from all this (my own words now) that the equation for voltage, as defined by Kaplan, would be ∆V = ∆U/q, or in words: the electric potential difference (∆V) between two points in an electric field (Ub/q - Ua/q) where 'q' is the same charge, or ∆U/q.
I hope this is good enough of a rationale
