Q 12-02-027NEETJEE MainTop questionMedium
A capacitor is charged by a battery and then disconnected. A dielectric slab of constant $K$ is now inserted to fill the gap. Which of the following is true?
Answer: (D) The charge stays the same, and the energy becomes $\dfrac{1}{K}$ times
Concept. Disconnected: $Q$ fixed; $C \to KC$.
Step 1. Energy. $U = \dfrac{Q^2}{2C} \to \dfrac UK$.
Answer. The charge stays the same, and the energy becomes $\dfrac1K$ times (Option D).
Solution by Sreeraj P, M.Sc Physics