A parallel plate capacitor C with plates of unit area and separation d is filled with a liquid of dielectric constant `K=2`. The level of liquid is `d//3` initially. Suppose the liquid level decreases at a constant speed v, the time constant as a function of time t is-

Options

A. `(6 in _0 R)/( 5d+ 3Vt) `
B. ` ( ( 15d + 9Vt)in _0R)/( 2d^(2) -3d Vt-9V^(2) t^(2) ) `
C. ` (6in _0R)/( 5d-3Vt) `
D. ` ( ( 15d -9Vt)in _0 R)/( 2d^(2) +3dVt-9V^(2)t^(2)) `

Answer

A