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

Shown in the figure are two point charges $+Q$ and $-Q$ inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If $\sigma_1$ is the surface charge density on the inner surface and $Q_1$ is the net charge on it,and $\sigma_2$ is the surface charge density on the outer surface and $Q_2$ is the net charge on it,then:

Five identical conducting plates,each of face area $A$,are placed parallel to each other with a separation of $d$ between two adjacent plates as shown in the figure. The plates $M$ and $N$ are given charges $Q_1$ and $Q_2$ respectively and the remaining plates are neutral. If the outermost plates are grounded,the potential difference between the plates $M$ and $N$ is . . . . . .

Two metal spheres $A$ and $B$ of radii $a$ and $b$ $(a < b)$ respectively are at a large distance apart. Each sphere carries a charge of $100 \mu C$. The spheres are connected by a conducting wire,then

‘The interior of a conductor can have no excess charge in the static situation’. Explain.

The dimensions of an atom are of the order of an $\mathring{A}$ $(10^{-10} \ m)$. Thus,there must be large electric fields between the protons and electrons. Why,then,is the electrostatic field inside a conductor zero?