Explain why a charge inside a cavity of a conductor does not experience any force due to a charge outside it.

(i) uniformly charged rod of finite length at a point along its length.

(iii) uniformly charged ring at a point on its axis.

(iv) uniformly charged disc at a point on its axis. Also show what happens when the distance of the field point is very large compared to its radius.

(v) infinite plane sheet of charge with uniform surface charge density at a point near to it.