A metallic rod is placed in a uniform electric field. Select the correct option.

Two metal spheres, one of radius $R$ and the other of radius $2R$, both have same surface charge density $\sigma $. They are brought in contact and separated. What will be new surface charge densities on them ?

Aspherical shell with an inner radius $'a'$ and an outer radius $'b' $ is made of conducting material. Apoint charge $+Q$ is placed at the centre of the spherical shell and a total charge $- q $ is placed on the shell.

Assume that the electrostatic potential is zero at an infinite distance from the spherical shell. The electrostatic potential at a distance $R$ $(a < R < b)$ from the centre of the shell is (where $K = $ $\frac{1}{{4\pi {\varepsilon _0}}}$)

An empty thick conducting shell of inner radius $a$ and outer radius $b$ is shown in figure.If it is observed that the inner face of the shell carries a uniform charge density $-\sigma$ and the surface carries a uniform charge density $ '\sigma '$

If the outer surface of the shell is earthed, then identify the correct statement(s)

Obtain an expression for electric field at the surface of a charged conductor.