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: $(I: r < a, II: a < r < b, III: r > b)$

Three identical uncharged metal spheres are at the vertices of an equilateral triangle. One at a time,a small sphere is connected by a conducting wire with a large metal sphere that is charged. The center of the large sphere is on the straight line perpendicular to the plane of the equilateral triangle and passing through its center (see figure). As a result,the first small sphere acquires charge $q_1$ and the second acquires charge $q_2$ $(q_2 < q_1)$. The charge that the third sphere $q_3$ will acquire is (Assume $l >> R$,$l >> r$,$d >> R$,$d >> r$):

$A$ spherical conductor of radius $2 \, m$ is charged to a potential of $120 \, V$. It is now placed inside another hollow spherical conductor of radius $6 \, m$. Calculate the potential to which the bigger sphere would be raised. (in $, V$)

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

$A$ metal cube is given a positive charge $(+Q)$. Which of the following statements is true?

Explain electrostatic shielding with a necessary diagram.