A parallel plate capacitor has capacitance \(C\), when there is vacuum within the parallel plates. A sheet having thickness \(\left(\dfrac{1}{3}\right)^{\mathrm{rd}}\) of the separation between the plates and relative permittivity \(K\) is introduced between the plates. The new capacitance of the system is:
1. \(\dfrac{3 {KC}}{2 {K}+1}\)
2. \(\dfrac{C K}{2+K}\)
3. \(\dfrac{3 {CK}^2}{(2 {K}+1)^2}\)
4. \(\dfrac{4 {KC}}{3{K}-1}\)