Two spheres of radius $R$ and $2R$ having charge $Q$ and $2Q$ respectively are placed far away from each other. How much charge will flow when key $k$ is pressed?

By keeping a conductor in an external electric field and from the results obtained by electrostatics,which of the following options is wrong?

Prove that,if an insulated,uncharged conductor is placed near a charged conductor and no other conductors are present,the uncharged body must be intermediate in potential between that of the charged body and that of infinity.

Two spheres of radius $a$ and $b$ respectively are charged and joined by a wire. The ratio of the electric field at the surfaces of the spheres is

Assertion $:-$ The maximum charge that can be given to a conductor of fixed volume depends on its shape.
Reason $:-$ If the electric field near the conductor is sufficient for dielectric breakdown of air,no more charge can be transferred to it.

An empty thick conducting shell of inner radius $a$ and outer radius $b$ is shown in the figure. If it is observed that the inner face of the shell carries a uniform charge density $-\sigma$ and the outer surface carries a uniform charge density $\sigma'$,if the outer surface of the shell is earthed,then identify the correct statement$(s)$.