The electrostatic field of a long uniformly charged wire varies with distance $r$ according to which relation?

$A$ positive charge $Q$ is placed on a conducting spherical shell with inner radius $R_1$ and outer radius $R_2$. $A$ particle with charge $q$ is placed at the center of the spherical cavity. The magnitude of the electric field at a point in the cavity,at a distance $r$ from the center,is

$A$ spherical shell with an inner radius $a$ and an outer radius $b$ is made of conducting material. $A$ point charge $+Q$ is placed at the centre of the spherical shell and a total charge $-q$ is placed on the shell. Charge $-q$ is distributed on the surfaces as:

Electric field produced due to an infinitely long straight uniformly charged wire at a perpendicular distance of $2 \ cm$ is $3 \times 10^8 \ N C^{-1}$. Then,linear charge density on the wire is . . . . . . . $(k = 9 \times 10^9 \ SI \ unit)$ (in $\mu C/m$)

An electron revolves around an infinite cylindrical wire having a uniform linear charge density of $2 \times 10^{-8} \, C \cdot m^{-1}$ in a circular path under the influence of an attractive electrostatic field,as shown in the figure. The velocity of the electron with which it is revolving is $......... \times 10^6 \, m \cdot s^{-1}$. (Given: mass of electron $= 9 \times 10^{-31} \, kg$)

Obtain the expression for the electric field due to a uniformly charged spherical shell at a point outside it.