Choose the correct statements from the following :
(A) For a point charge, concentric spheres centred at the location of the charge are equipotential surfaces
(B) For practical purpose the earth is used as a reference at zero potential in electrical circuit
(C) In a cavity within a conductor without charges, the electric field is zero
(D) During charging by rubbing, the insulating material with higher work function becomes positively charged
(E) Dielectric polarisation means formation of electric dipole inside the dielectric
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (B), (C) and (E)
An equipotential surface is a surface on which the potential has the same value everywhere; the field is perpendicular to it.
(A) For a point charge, concentric spheres centred at the location of the charge are equipotential surfaces — Correct. \( V = q/(4\pi\varepsilon_0 r) \) depends only on the distance \( r \), so every sphere centred on the charge is an equipotential.
(B) For practical purpose the earth is used as a reference at zero potential in electrical circuit — Correct. The earth is a very large conductor whose potential hardly changes, so it is taken as the zero of potential.
(C) In a cavity within a conductor without charges, the electric field is zero — Correct. The field inside a charge-free cavity is zero whatever lies outside; this is electrostatic shielding.
(D) During charging by rubbing, the insulating material with higher work function becomes positively charged — Incorrect. On rubbing, electrons move to the material with the higher work function, so the material with the higher work function becomes negatively charged.
(E) Dielectric polarisation means formation of electric dipole inside the dielectric — Correct. In an external field the molecules become dipoles or their dipoles line up, so the dielectric develops a net dipole moment.
NCERT (2026-27):
Equipotential Surfaces – “… This shows that V is a constant if r is constant. Thus, equipotential surfaces of a single point charge are concentric spherical surfaces centred at the charge.”
Electrostatics of Conductors – “… 6. Electrostatic shielding Consider a conductor with a cavity, with no charges inside the cavity. A remarkable result is that the electric field inside the cavity is zero, whatever be the size and shape of the cavity and whatever be the charge on the conductor and the external fields in which it might be placed.”
Dielectrics and Polarisation – “… The non-polar molecule thus develops an induced dipole moment. The dielectric is said to be polarised by the external field.”