Consider a parallel plate capacitor of capacity 10 $\mu\: F$ filled with air. When the gap between the plates is filled partly with a dielectric constant 4, as shown in figure.The new capacity of the capacitor is ( A is the area of plates ) :

Question

$\begin {array} {1 1} (1)\;20\: \mu\: F & \quad (2)\;40\: \mu\: F \\ (3)\;2.5\: \mu\: F & \quad (4)\;25\: \mu\: F \end {array}$