Identify the correct statements among the following:
(A) The value of the electrostatic force constant, k depends on the medium between the two charges and on the choice of system of units.
(B) For two positively charged bodies, one more highly charged than the other, the force between them may be attractive.
(C) The charge on a body does change with its velocity.
(D) An electric dipole is a pair of two equal and similar charges placed at a very small distance.
Choose the correct answer from the following options:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (B) only
(A) The value of the electrostatic force constant, k depends on the medium between the two charges and on the choice of system of units. — Correct. \( k = 1/(4\pi\varepsilon) \) uses the permittivity of the medium, and its value changes with the units.
(B) For two positively charged bodies, one more highly charged than the other, the force between them may be attractive. — Correct. In extended conducting bodies the more highly charged body induces negative charge on the near side of the other, which can make the force attractive at close range.
(C) The charge on a body does change with its velocity. — Incorrect. Charge is invariant: it does not depend on the speed of the body.
(D) An electric dipole is a pair of two equal and similar charges placed at a very small distance. — Incorrect. A dipole is a pair of equal and opposite charges.
Statements (A) and (B) are correct, which is Option (2).
Note: Statement (B) is correct only for extended conducting (or polarisable) bodies. For point charges, Coulomb's law gives a repulsive force between any two positive charges, and then only (A) would be correct, which is Option (4).