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 capac…

Question

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?

Accepted Answer

Correct answer: D. (d) When a parallel plate air capacitor connected to a cell of emf V, then charge stored will be q= CV ⇒V= qC Also, energy stored is U= 12CV^2= q^22C As the battery is disconnected from the capacitor the charge will not be destroyed, i.e. q^ '=q with the introduction of dielectric in the gap of capacitor the new capacitance will be C^ '= CK ⇒V^ '= qC^ '= q CK The new energy stored will be U^ '= 12C^ ' (V^ ' )^2= q^22 CK U=U^ '-U = q^22C( 1K-1) = 12CV^2( 1K-1)

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

Solution

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