## richyw 3 years ago An isolated conducting sphere with radius $$R=6.85\text{cm}$$ has charge $$Q=1.25nC$$ a) how much potential energy is stored in the electric field of this charged conductor? b)what is the energy density at the surface of the sphere? c)what is the radius $$R_0$$ of an imaginary spherical surface such that half of the stored potential energy lies within it?

my attempts: a)$U=\frac{Q^2}{2C}=\frac{Q^2}{8\pi\epsilon_0R}$b)$u=\frac{1}{2}\epsilon_0E^2$$u=\frac{1}{2}\epsilon_0\left(\frac{1}{4\pi\epsilon_0}\frac{Q}{R^2}\right)^2$$u=\frac{Q^2}{32\pi^2\epsilon_0R^4}$ c) unsure!