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

Two infinitely long thin straight parallel wires are kept at a perpendicular distance of $2R$,having uniform linear charge densities $+\lambda$ and $-\lambda$ respectively. The magnitude of the electric field at the midpoint between the two wires will be . . . . . . .

An $100 \ eV$ electron is fired directly towards a large metal plate having surface charge density $-2 \times 10^{-6} \ C \ m^{-2}$. The distance from where the electron is projected,so that it just fails to strike the plate,is: (in $mm$)

Two large,thin metal plates are parallel and close to each other. On their inner faces,the plates have surface charge densities of opposite signs and of magnitude $17.0 \times 10^{-22} \; C/m^2$. What is $E$:
$(a)$ in the outer region of the first plate,
$(b)$ in the outer region of the second plate,and
$(c)$ between the plates?

Two concentric conducting thin spherical shells of radii $a$ and $b$ $(b > a)$ are given charges $Q$ and $-2Q$ respectively. The electric field along a line passing through the centre as a function of distance $(r)$ from the centre is given by:

Which of the following graphs shows the variation of electric field $E$ due to a hollow spherical conductor of radius $R$ as a function of distance $r$ from the centre of the sphere?