Answer: kQr/R3.
- A kQ/r2 (same as outside)
- B kQr/R3
- C Zero
- D kQ/R2 x r
Correct answer: B. kQr/R3
Explanation: Inside solid sphere: only the charge within radius r contributes. Qenclosed = Q(r/R)3. E = kQ_enclosed/r2 = kQr/R3.
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.