AIPMT | 2015CapacitanceEasy
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 ?
Options
A.The energy stored in the capacitor decreases K times.
B.The change in energy stored is 
C.The charge on the capacitor is not conserved.
D.The potential difference between the plates decreases K times.
Solution
Once the capacitor is charged, its charge will be
constant Q = CV
When dielectric slab is inserted
CNew = KC
E =
⇒ ENew = 
Einitial
V =
so VNew = 
V
Hence option (3)
constant Q = CV
When dielectric slab is inserted
CNew = KC
E =
⇒ ENew = EinitialV =
so VNew = VHence option (3)
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