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?

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?, The potential difference between the plates decreases K times., The energy stored in the capacitor decreases K times., The change in energy stored is 1 2 C V 2 1 K - 1 ., The charge on the capacitor is not conserved.

MARKS App · Accepted Answer

For air K = 1 , C 1 = C q = C 1 V … i . The charge remains constant. U 1 = q 2 2 C U 2 = q 2 2 C K Change in energy stored in the capacitor, U = U 2 - U 1 = q 2 2 C 1 K - 1 = 1 2 C V 2 1 K - 1 V ' = q C K ⇒ V ' = V K Here,1- Potential difference between the plates decreases by K times. 2- The change in energy stored ∆ U = 1 2 C V 2 1 K - 1 . 3- Charge is conserved. 4- The energy stored in capacitor decrease by K , U 2 = 1 2 q 2 C K .

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