Giải Ta có: \(\left. {\matrix{{W = {1 \over 2}C{U^2}} \cr {C = {{\varepsilon S} \over {{{9.10}^9}.4\pi d}}} \cr
{U = E.d} \cr} } \right\} \Rightarrow W = {1 \over 2}.{{\varepsilon S} \over {{{9.10}^9}.4\pi d}}.{E^2}{d^2}\)\( \Rightarrow W = {{\varepsilon Sd{E^2}} \over {{{9.10}^9}.8\pi }} \Rightarrow \) \(W = {{\varepsilon {E^2}V} \over {{{9.10}^9}.8\pi }}\)
