A parallel plate capacitor has plate of length 'l' width 'w' and separation of plates is 'd' . It is connected to a battery of emf V . A dielectric slab of the same thickness 'd' and of dielectric constant k=4 is being inserted between the plates of the capacitor . At what lenght of the slab inside plates , will the energy stored in the capacitor be two time the initial energy stored ?

Options

A. `2l//3`
B. `l//3`
C. `l//4`
D. `l//2`