Which of the following statements are correct ?
A. The electric field inside uniformly charged spherical shell is zero.
B. In a non-polar molecule, the centres of positive and negative charges do not coincide.
C. In a uniform electric field, a dipole experiences a torque but experiences no net force.
D. When a dielectric is inserted fully between the plates of a capacitor, then its capacitance decreases.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A and C only
(A) The electric field inside uniformly charged spherical shell is zero. — Correct. By Gauss's law, a Gaussian surface inside the shell encloses no charge, so the field inside is zero.
(B) In a non-polar molecule, the centres of positive and negative charges do not coincide. — Incorrect. In a non-polar molecule the two centres coincide, so it has no permanent dipole moment. In a polar molecule they are separated.
(C) In a uniform electric field, a dipole experiences a torque but experiences no net force. — Correct. The two equal and opposite charges feel equal and opposite forces, so the net force is zero, but the forces form a couple of torque \( \vec{\tau} = \vec{p}\times\vec{E} \).
(D) When a dielectric is inserted fully between the plates of a capacitor, then its capacitance decreases. — Incorrect. A dielectric of constant K reduces the field between the plates, so the potential difference falls for the same charge and the capacitance increases to \( C' = KC \).
NCERT (2026-27):
Potential Due to a System of Charges – “… The electric field inside the shell is zero.”
Dielectrics and Polarisation – “… In a non-polar molecule, the centres of positive and negative charges coincide.”
Summary – “… 13. In a uniform electric field E, a dipole experiences a torque \( \tau \) given by \( \tau = \mathbf{p} \times \mathbf{E} \) but experiences no net force.”
Effect of Dielectric on Capacitance – “… Thus, the dielectric constant of a substance is the factor (>1) by which the capacitance increases from its vacuum value, when the dielectric is inserted fully between the plates of a capacitor.”