The energies required to set up in a cube of side 10   cm , ( a ) A uniform electric field of 10 7…

Recall the formula of energy in terms of electric field and magnetic field strength,

$$\begin{gathered} E_E=\frac{1}{2}{\epsilon }_0{\left(E\right)}^{2}V \& E_B=\frac{1}{2}{\epsilon }_0{\left(Bc\right)}^{2}V \\ \Rightarrow E_E=\frac{1}{2}{\epsilon }_0{\left(E\right)}^{2}V \\ \Rightarrow E_E=\frac{1}{2}\times 8.9\times {10}^{-12}\times {\left({10}^7\right)}^2\times {10}^{-3}=0.445 \mathrm{J} \\ \Rightarrow E_B=\frac{1}{2}{\epsilon }_0{\left(Bc\right)}^{2}V \\ \Rightarrow E_B=\frac{1}{2}\times 8.9\times {10}^{-12}\times {\left(0.25\right)}^2\times {\left(3\times {10}^8\right)}^2\times {10}^{-3}=25 \mathrm{J} \end{gathered}$$