Solution
For a single point charge, the electric field vectors at any two points must satisfy two conditions:
- Direction: The vectors must be radial, meaning they must point directly away from (or towards) a single common point (the source charge).
- Magnitude: The field strength decreases with distance ($E \propto 1/r^2$). Thus, the vector at the point closer to the source must be longer.
Analysis:
- Figure (a): The vectors at A and B diverge from a common point to the left. Point B is closer to this intersection point and has a longer vector than A. This is consistent with a point charge.
- Figure (c): The vectors are concurrent. This implies the source is on the same intersection point. The vector at B is longer than A, implying the source is closer to B. This is consistent with a point charge.
- Figures (b) and (d) show vector directions that cannot intersect at a single source point consistent with the magnitude rules.
Answer: (a) and (c)