A student sketches the equipotential map for two point charges of equal magnitude but…
PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A student sketches the equipotential map for two point charges of equal magnitude but opposite sign separated by 4cm along the x-axis. In the sketch, each charge is surrounded by perfect concentric circles that do not distort or merge as they extend into the space between the charges. Which statement best explains why this sketch cannot represent the actual equipotential distribution?
(a) Concentric circles would indicate both charges have the same sign; since one charge is negative, no closed equipotential circles can surround it.
(b) Because the equal and opposite charges cancel each other's potential everywhere between them, the entire space between the charges is one equipotential surface, so no equipotential lines should be drawn there.
(c) The sketch ignores that potentials from the two charges add, so points equidistant from one charge are at different potentials depending on their distance from the other charge.
(d) Equipotential lines for two point charges must be straight lines that run between the charges, so curved circles cannot be correct.