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

Answer

C

Explanation

(c ) If a dielectric slab of dielectric contant `K` is filled in between the plates of a condenser while charging it, the potential difference between the plates does not change but the capacity becomes `K` times, therefore `V' = V, C' = KC`
`:.` Energy stored in the capacitor
`U' = (1)/(2) C 'V'^(2)`
`= (1)/(2) (KC) (V^(2))`
`= [(1)/(2) CV^(2)] K = KU`
Thus, energy stored becomes `K` times. surface charge denstiy
`sigma' = (q')/(A) = (C' V')/(A) = (KCV)/(A) = K (q)/(A) = K sigma`