A hollow insulated conducting sphere is given a positive charge of $10 \mathrm{\mu C}$. What will be the electric field at the centre of the sphere? The radius of the sphere is $2 \mathrm{m}$.

Consider a region in free space bounded by the surfaces of an imaginary cube having sides of length $a$ as shown in the figure. A charge $+Q$ is placed at the centre $O$ of the cube. $P$ is such a point outside the cube that the line $OP$perpendicularly intersects the surface $ABCD$ at $R$ and also $OR=RP=a/2$. A charge $+Q$ is placed at point $P$ also. What is the total electric flux through the five faces of the cube other than $ABCD?$

Two isolated charged metallic spheres of radii $R_1$ and $R_2$ having charges $Q_1$ and $Q_2$, respectively, are connected to each other, then there is:

A parallel plate capacitor of capacitance $C$ is as shown. A thin metal plate $A$ is placed between the plates of the given capacitor in such a way that its edges touch the two plates as shown. The capacity a cross $P$ and $Q$now becomes