Electric Potential
High-Yield Summary
- 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?