One plate of a capacitor is fixed, and the other is connected to a spring as shown in. Area of both the plates is `A` In strady state (equilibrium), separation between the plates is `0.8d` (spring was unstretched , and the distance between the plates was `d` when capacitor was uncharged). The force conntant of the spring is approximately.

Options

A. `(4 in_(0)AE^(2))/(d^(3))`
B. `(2 in_(0)AE)/(d^(2))`
C. `(6 in_(0) E^(2))/(Ad^(3))`
D. `(in_(0)AE^(3))/(2d^(3))`

Answer

A

Explanation

`(q^(2))/(2A in_(0))=kx ,((CE)^(2))/(2 A in_(0))=k(d-0.8d),C=(in_(0)A)/(0.8d)`
`K=(4 in_(0) AE^(2))/(d^(3))`.