$A$ charge $+q$ is placed somewhere inside the cavity of a thick conducting spherical shell of inner radius $R_1$ and outer radius $R_2$. $A$ charge $+Q$ is placed at a distance $r > R_2$ from the centre of the shell. Then the electric field in the hollow cavity

Charge on the outer sphere is $q$ and the inner sphere is grounded. The charge on the inner sphere is $q'$,for $(r_2 > r_1)$. Then

Write important results regarding the electrostatics of conductors.

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.

Two charged spheres of radius $R_1$ and $R_2$ respectively are charged and joined by a wire. The ratio of the electric field at the surfaces of the spheres is . . . . . . .

Two isolated metallic solid spheres of radii $R$ and $2R$ are charged such that both have the same charge density $\sigma$. The spheres are then connected by a thin conducting wire. If the new charge density of the bigger sphere is $\sigma^{\prime}$,then the ratio $\frac{\sigma^{\prime}}{\sigma}$ is: