Capacitor

If a slab of insulating material (conceptual). \(4 \times 10^{-3} \mathrm{~m}\) thick is introduced between the plates of a parallel plate capacitor, the separation between the plates has to be increased by \(3.5 \times 10^{-3} \mathrm{~m}\) to restore the capacity to original value. The dielectric constant of the material will be