$22\mathrm{.}35$ Negative charge

$$

$$

is distributed uniformly over the surface of a thin spherical insulating shell with radius

$$

$.$

Calculate the force $($magnitude and direction$)$ that the shell exerts on a positive point charge

$$

located a distance $($a$)$

$$

$>$

$$

from the center of the shell $($outside the shell$)$; $($b$)$

$$

$<$

$$

from the center of the shell $($inside the shell$).$

$22\mathrm{.}36$ A long line carrying a uniform linear charge density

$+$

$50\mathrm{.}0$

$$

$$

C

$/$

$$

runs parallel to and $10\mathrm{.}0$ cm from the surface of a large, flat plastic sheet that has a uniform surface charge density of

$$

$100$

$$

$$

C$/$m

$2$

on one side. Find the location of all points where an

$$

particle would feel no force due to this arrangement of charged objects.