A parallel plate capacitor filled with oil of dielectric constant \( k = 3 \), has a capacitance \( C \). After removing the oil between the plates, the capacitance of the capacitor will become
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( \displaystyle\frac{1}{3}C \)
Filling the gap of a parallel plate capacitor with a dielectric multiplies its capacitance by the dielectric constant \( k \).
\( \displaystyle C = k\,C_0 = \frac{k\,\varepsilon_0 A}{d} \)
Removing the oil leaves the air-filled capacitor, whose capacitance \( C_0 \) is the one without the factor \( k \).
\( \displaystyle C_0 = \frac{C}{k} = \frac{C}{3} \)
NCERT (2026-27):
Effect of Dielectric on Capacitance – “… From Eqs. (2.46) and (2.51)
\( \displaystyle C = K C_0 \qquad (2.54) \)
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.”