Electric potential: V = U/q = kQ/r — potential energy per unit charge at a location, independent of which test charge (if any) is placed there.
SI unit: volt (V) = 1 joule/coulomb.
Unlike U (a pair-of-charges quantity), V depends only on the source charge and location — the same for any test charge placed there.
Potential difference (voltage): ΔV = Vb − Va = Wab/q — work needed to move a charge between two points; drives current in circuits.
Sits alongside Fe, E, and U as related-but-distinct descriptions of the same charge system.
Electric Potential and Potential Difference
V = U/q = kQ/r | ΔV = Vb − Va = Wab/q
V = Electric potential, in volts
U = Electric potential energy
q = Test charge magnitude
Q = Source charge
r = Distance from source charge
ΔV = Potential difference (voltage) between points a and b
Wab = Work done moving charge q from a to b
Four Related Electrostatic Quantities
Quantity
Formula / Unit
Electrostatic force (Fe)
kq1q2/r² — newton (N)
Electric field (E)
kQ/r² — N/C or V/m
Electric potential energy (U)
kQq/r — joule (J)
Electric potential (V)
kQ/r — volt (V)
Common MCAT Trap
V = kQ/r looks like U = kQq/r without the q — remember V is per unit charge (location-only), while U depends on a specific test charge's magnitude.
Voltage (ΔV) is what drives current, not electric potential (V) alone at a single point — always check whether a question wants an absolute potential or a difference.
Quick Recall
How does electric potential differ from electric potential energy?
What does potential difference (voltage) between two points represent?
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