In this problem, you can show from Coulomb's law that the constant of proportionality in Gauss's law must be $1 / \epsilon_{0} .$ Imagine a sphere with its center at a point charge
q. (a) Write an expression for the electric flux in terms
of the field strength $E$ and the radius $r$ of the sphere. [Hint: The field strength $E$ is the same everywhere on the sphere and the field lines cross the sphere perpendicular to its surface.] (b) Use Gauss's law in the form $\Phi_{\mathrm{E}}=c q(\text { where } c$ is the constant of proportionality) and the electric field strength given by Coulomb's law to show that $c=1 / \epsilon_{0}$