Which of the following materials is used as a dielectric between the plates of a parallel plate capacitor to increase its capacitance?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Mica
A dielectric is a non-conducting substance. Filling the space between the plates with it raises the capacitance by the factor \( K \), the dielectric constant.
Option (1) Copper — Incorrect. Copper is a metal with free electrons. It is a conductor and not a dielectric. A copper filling touching both plates would join them and discharge the capacitor.
Option (2) Stainless steel — Incorrect. Stainless steel is an alloy of iron, a metal that conducts electricity, so it is not a dielectric.
Option (3) Mica — Correct. Mica is an insulator. The field between the plates polarises it. This reduces the field and the potential difference for the same charge, so the capacitance \( C=K\varepsilon_0A/d \) increases.
Option (4) Tin — Incorrect. Tin is a metal and conducts electricity, so it cannot serve as a dielectric.
NCERT (2026-27):
Dielectrics and Polarisation – “Dielectrics are non-conducting substances. In contrast to conductors, they have no (or negligible number of ) charge carriers.”
Effect of Dielectric on Capacitance – “…
\( \displaystyle K=\frac{C}{C_0} \qquad (2.54) \)
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.”