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Question 31582
JEE Physics · Hard

Capacitance: Energy Minimisation MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Energy MinimisationHardQuestion 31582

Question

When a dielectric slab is inserted into an isolated capacitor (no battery), the system's energy:
  1. A
    Increases
  2. B
    Decreases
    Correct
  3. C
    Stays constant
  4. D
    First increases then decreases

Correct answer

Decreases

Explanation

With Q fixed, U = Q²/2C. Inserting dielectric increases C, so U decreases. The energy released does work pulling the slab in — the slab is always attracted in for an isolated capacitor.

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