I keep getting “Potential as energy per charge” questions wrong in Electrostatic Potential & Capacitance. What's the trap?
adding potentials as vectors or dropping the sign of a negative source charge.
The usual trap: adding potentials as vectors or dropping the sign of a negative source charge. How to avoid it: fields need directions; potentials need signs. Go back to the definition — Electric potential at a point is potential energy per unit test charge. Because it is a scalar, contributions from many source charges add algebraically with their signs.
Key point
Potential as energy per charge
Common mistake
adding potentials as vectors or dropping the sign of a negative source charge.
Memory tip
fields need directions; potentials need signs.
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