$A$ point charge is kept at the centre of a metallic insulated spherical shell. Then:

As shown in the figure,a point charge $Q$ is placed at the centre of a conducting spherical shell of inner radius $a$ and outer radius $b$. The electric field due to charge $Q$ in three different regions $I$,$II$,and $III$ is given by: $(I: r < a, II: a < r < b, III: r > b)$

Conduction electrons are almost uniformly distributed within a conducting plate. When placed in an electrostatic field $\overrightarrow{E}$,the electric field within the plate

Two charged spherical conductors of radii $R_1$ and $R_2$ are connected by a wire. The ratio of surface charge densities of the spheres $\sigma_1/\sigma_2$ will be

Two conducting spheres of radii $20\, cm$ and $15\, cm$ are placed on insulating stands. Both are given an equal charge of $10\ \mu C$. When they are connected by a copper wire and then disconnected,which of the following is true?

$(a)$ $A$ conductor $A$ with a cavity as shown in Figure $(a)$ is given a charge $Q$. Show that the entire charge must appear on the outer surface of the conductor.
$(b)$ Another conductor $B$ with charge $q$ is inserted into the cavity keeping $B$ insulated from $A$. Show that the total charge on the outside surface of $A$ is $Q+q$ [Figure $(b)$].
$(c)$ $A$ sensitive instrument is to be shielded from the strong electrostatic fields in its environment. Suggest a possible way.