Answer: 6 × 10-3 J.
- A 3 × 10-3 J
- B 6 × 10-3 J
- C 9 × 10-3 J
- D 1.2 × 10-2 J
Correct answer: B. 6 × 10-3 J
Explanation: U = -pE cosθ, so ΔU = -pE(cos120° - cos60°) = -pE(-0.5 - 0.5) = pE = 3 × 10-8 × 2 × 105 = 6 × 10-3 J.
Field lines always point from positive to negative charge, are denser where the field is stronger, and never cross; an isolated positive charge has lines radiating symmetrically outward, while a dipole's lines curve from the positive to the negative charge.
Concept context
Coulomb's law, electric field, potential, capacitors, Gauss's law.