(II) A spherical rubber balloon carries a total charge $Q$ uniformly distributed on its surface. At $t=0$ the nonconducting balloon has radius $r_{0}$ and the balloon is then slowly blown up so that $r$ increases linearly to 2$r_{0}$ in a time $T$ . Determine the electric field as a function of time $(a)$ just
outside the balloon surface and $(b)$ at $r=3.2 r_{0} .$