A certain atom has $85$ protons. Assume that the nucleus is a sphere with radius $7\mathrm{.}12fm$ and with the charge of the protons uniformly

spread through the sphere. At the nucleus surface what are $($a$)$ the magnitude and $($b$)$ direction $($radially inward or outward$)$ of the

electric field produced by the protons?

$($a$)$ Number

Units

$($b$)$