Assertion : A parallel plate capacitor is connected across battery through a key. A dielectric slab dielectric constant `K` is introduced between the plates. The energy which is stored becomes `K` times.
Reason : The surface density of charge on the plate remains constant or uncharged.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both are false

Answer

C

Explanation

V = Constant `=V_0`
`U=1/2CV^2 =1/2 (kC_0)V_0^2=k(1/2C_0V_0^2)=kU_0`
Surface charge density `(Sigma.) = (kq)/A=ksigma`