Question

Assertion : When a dielectric slab is gradually inserted between the plates of an isolated parallel-plate capacitor, the energy of the system decreases.
Reason : The force between the plates decreases

• A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
• B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
• C. If the Assertion is correct but Reason is incorrect.
• D. If the Assertion is incorrect and Reason is correct.

Answer 1

Answer: (C)

$C^{\prime}=k C$, and $U^{\prime}=\frac{q^2}{2 C^{\prime}}=\frac{q^2}{2 k C}$. With the introduction of dielectric, energy of the system decreases. As charge on the capacitor remains same, and so force between them remains same.