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 charged spherical conductors of radius $R_{1}$ and $R_{2}$ are connected by a wire. Then the ratio of surface charge densities of the spheres $(\sigma_{1} / \sigma_{2})$ is:

$A$ solid spherical conducting shell has inner radius $a$ and outer radius $2a$. At the center of the shell, a point charge $+Q$ is located. What must the charge of the shell be in order for the charge density on the inner and outer surfaces of the shell to be exactly equal?

Two metallic spheres of radii $a$ and $b$ are placed far away from each other and are connected by a thin conducting wire. The total charge on them is $Q$. Calculate the potential of each sphere.

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

'At the surface of a charged conductor,the electrostatic field must be normal to the surface at every point'. Explain.