A metal foil of negligible thickness is introduced between two plates of a capacitor at the centre. The new capacitance of the capacitor would be:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → C
A metal foil in the gap becomes an equipotential surface and splits the capacitor into two capacitors in series, each with the same plate area \( A \) and half the gap, \( d/2 \). Originally \( C = \frac{\varepsilon_0A}{d} \).
\( \displaystyle C_1 = C_2 = \frac{\varepsilon_0A}{d/2} = 2C \)
\( \displaystyle \frac{1}{C_{\mathrm{new}}} = \frac{1}{2C} + \frac{1}{2C} = \frac{1}{C} \Rightarrow C_{\mathrm{new}} = C \)
Note: A similar question was also asked in CUET (UG) 2026 on 18-05-2026 (Slot 2), and in CUET (UG) 2023 on 07-06-2023 (Slot 3).