Figure shows a solid hemisphere with a charge of $5 \mathrm{nC}$ distributed uniformly through its volume. The hemisphere lies on a plane and point $P$ is located on the plane along a radial line from the centre of curvature at distance $15 \mathrm{cm}.$ The electric potential at point $P$ due to the hemisphere is, 

Two concentric uniformly charged spheres of radii $10 \mathrm{cm}$ and $20 \mathrm{cm}$ are arranged as shown in figure. The potential difference between the spheres is,

Coulomb's constant $K=9\times {10}^{10} \mathrm{kg} {\mathrm{m}}^3 {\mathrm{s}}^{-2}{\mathrm{C}}^{-2}$

The capacitance of a parallel plate capacitor with air as dielectric is $C$. If a slab of dielectric constant $K$ and of the same thickness as the separation between the plates is introduced so as to fill ${\frac{1}{4}}^{\mathrm{th}}$ of the capacitor (shown in figure), then the new capacitance is,

As shown in the figure, charges $+q$ and $-q$ are placed at the vertices $B$ and $C$ of an isosceles triangle. The potential at the vertex $A$ is,