A parallel plate air capacitor of capacitance C is connected to a cell of emf V and then disconnected from it. A dielectric slab of dielectric constant K, which can just fill the air gap of the capacitor, is now inserted in it. Which of the following is incorrect?

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The change in energy stored is 12CV21K-1 .

The charge on the capacitor is not conserved.

The potential difference between the plates decreases K times.

The energy stored in the capacitor decreases K times.

answer is B.

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Detailed Solution

Due to dielectric insertion, new capacitance C2=CK Initial energy stored in capacitor, U1=q22C Final energy stored in capacitor, U2=q22KCChange in energy stored, ΔU=U2-U1ΔU=q22C1K-1=12CV21K-1New potential difference between plates V'=qCK=VK

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