A non uniformly shaped conductor is charged then at it's sharpest point

An empty thick conducting shell of inner radius $a$ and outer radius $b$ is shown in figure.If it is observed that the inner face of the shell carries a uniform charge density $-\sigma$ and the surface carries a uniform charge density $ '\sigma '$

If the charge $q_A$ is slowly moved inside the shell, then choose the statement$(s)$

The electric field near a conducting surface having a uniform surface charge density $\sigma $ is given by

A conducting sphere of radius $r$ has a charge. Then

Consider the shown system of two concentric thin metal shells. The inner hell has charge $Q$, while the outer shell is neutral. Potential difference between the shells is $V$. If the shell are joined by metal wire, then potential of the inner shell is

$A$ and $B$ are two concentric spheres. If $A$ is given a charge $Q$ while $B$ is earthed as shown