Two metallic concentric shells are shown. Before closing the switch,the charge on the inner shell is $Q$ and the charge on the outer shell is $2Q$. The potential at point $A$ is $V$. What will be the potential at the same point after closing the switch?

$A$ hollow closed conductor of irregular shape is given some charge. Which of the following statements are correct?

Given below are two statements $:$ one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ The outer body of an aircraft is made of metal which protects persons sitting inside from lightning strikes.
Reason $(R) :$ The electric field inside the cavity enclosed by a conductor is zero.
In the light of the above statements,choose the most appropriate answer from the options given below.

$A$ point charge $q$ is placed in a cavity in a metal block. If a charge $Q$ is brought outside the metal,then the electric force experienced by $q$ is

Two insulated charged spheres of radii $20\,cm$ and $25\,cm$ respectively and having an equal charge $Q$ are connected by a copper wire,then they are separated.

$A$ hollow metal sphere of radius $R$ is charged with a charge $Q$. The electric potential and intensity inside the sphere are respectively