A parallel plate capacitor is made of two square plates of side 'a', separated by a distance d (d<<a). The lower triangular portion is filled with a dielectric of dielectric constant K, as shown in the figure.

Capacitance of this capacitor is :

(1) ${1\over2}{k\in_0a^2\over d}$

(2) ${k\in_0a^2\over d}\ln K$

(3) ${k\in_0a^2\over d(K-1)}\ln K$

(4) ${k\in_0a^2\over 2d(K+1)}$

Capacitance of this capacitor is :

(1) ${1\over2}{k\in_0a^2\over d}$

(2) ${k\in_0a^2\over d}\ln K$

(3) ${k\in_0a^2\over d(K-1)}\ln K$

(4) ${k\in_0a^2\over 2d(K+1)}$