Example M2. A cloud of charge occupies the part of the sphere $$ x^2 + y^2 + z^2 \le a^2 $$ in which $z\ge\sqrt{x^2+y^2}$. The charge density at $(x,y,z)$ is $$ \rho_V(x,y,z) = 8\beta z\qquad\hbox{C/m${}^3$}, $$ for some constant $\beta$. Find

  1. the total charge in the cloud;
  2. an integral expression for the electric field ${\bf E}(x,y,z)$, valid for any point $(x,y,z)$ outside the cloud;
  3. exact values for two components of the vector ${\bf E}(0,0,z)$, assuming $z>a$; and
  4. an iterated double integral expression for the vector component not found in part (c).