Electrostatics deals with the study of forces, fields and potential arising from static charges. Which of the following statements are correct?
(A) Electrostatic force is a conservative force
(B) Charge is quantized because only integral number of electrons can be transferred from one body to the other
(C) In a uniform electric field \( E \), an electric dipole experiences a torque \( \tau \) and a net force \( F \).
(D) The electric field lines start from positive charges and end at negative charges. If there is a single charge, these may start or end at infinity.
(E) If the uniform surface charge density of an infinite plane sheet is positive, the electric field is directed away from the plate.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), (D) and (E) only
(A) Electrostatic force is a conservative force — Correct. The work done by it depends only on the end points, not on the path.
(B) Charge is quantized because only integral number of electrons can be transferred from one body to the other — Correct. Charge is gained or lost only in whole electrons, so \( q = ne \).
(C) In a uniform electric field \( E \), an electric dipole experiences a torque \( \tau \) and a net force \( F \). — Incorrect. The forces \( +qE \) and \( -qE \) give a torque \( \vec{p}\times\vec{E} \), but the net force is zero.
(D) The electric field lines start from positive charges and end at negative charges. If there is a single charge, these may start or end at infinity. — Correct. This is a basic property of field lines.
(E) If the uniform surface charge density of an infinite plane sheet is positive, the electric field is directed away from the plate. — Correct. The field \( \sigma/2\varepsilon_0 \) of a positive sheet points away from the sheet on each side.
NCERT (2026-27):
Introduction – “… Coulomb force between two (stationary) charges is also a conservative force.”
Quantisation of Charge – “… Thus the charge on any body is always an integral multiple of e and can be increased or decreased also in steps of e.”
Dipole in a Uniform External Field – “… The net force on the dipole is zero, since E is uniform. However, the charges are separated, so the forces act at different points, resulting in a torque on the dipole.”
Electric Field Lines – “… (i) Field lines start from positive charges and end at negative charges. If there is a single charge, they may start or end at infinity.”
Field Due to a Uniformly Charged Infinite Plane Sheet – “… E is directed away from the plate if σ is positive and toward the plate if σ is negative.”