$$\begin{gathered} 17) Two parallel plate of area A are separated by two different dielectrics ass shown in the fig \\ The net capaci\tan ce is \\ A) \frac{4{\in }_{0}A}{3d} B) \frac{3{\in }_{0}A}{4d} \\ C) \frac{2{\in }_{0}A}{d} B) \frac{{\in }_{0}A}{d} \end{gathered}$$

$$\begin{gathered} 19) A spherical capacitor is made of two conducting spherical shells of radii a and b. The \\ space between the shells is filled with a dielectric of dielectric cons\tan t K upto a radius c \\ as shown in the figure. calculate the capaci\tan ce. \\ A) \frac{2\mathrm{\pi }{\in }_0\mathrm{Kabc}}{\mathrm{Ka}\left(\mathrm{b}-\mathrm{c}\right)+b(c-a)} B) \frac{\mathrm{\pi }{\in }_0\mathrm{Kabc}}{2\mathrm{Ka}\left(\mathrm{b}-\mathrm{c}\right)+b(c-a)} \\ C) \frac{4\mathrm{\pi }{\in }_0\mathrm{Kabc}}{\mathrm{Ka}\left(\mathrm{b}-\mathrm{c}\right)+b(c-a)} D) \frac{\mathrm{Ka}\left(b-c\right)+b\left(c-a\right)}{4\mathrm{\pi }{\in }_0\mathrm{Kabc}} \end{gathered}$$