d
\(\mathrm{i}=\mathrm{i}_{0}\left(1-\mathrm{e}^{-\mathrm{R}t / \mathrm{L}}\right)=\mathrm{i}_{0}\left(1-\mathrm{e}^{-t / T_{\mathrm{C}}}\right)\)

\(\mathrm{q}=\int_{0}^{\mathrm{T}_{\mathrm{C}}} \mathrm{i} \mathrm{dt}\)

\(=\int_{0}^{T_{c}} \frac{\varepsilon}{R}\left(1-e^{-t / T_{c}}\right)\)

\(=\left.\frac{\varepsilon}{R}\left(t-\frac{e^{-t / T_{c}}}{-1 / T_{c}}\right)\right|_{0} ^{T_{c}}\)

\(=\frac{e}{R}\left(T_{c}-T_{c} e^{-1}\right)-\frac{e}{R}\left(0+T_{c}\right)\)

\(\mathrm{q}=\frac{\mathrm{e}}{\mathrm{R}} \times \mathrm{T}_{\mathrm{C}} \mathrm{e}^{-1}\)

\(=\frac{\varepsilon}{\mathrm{R}} \times \frac{\mathrm{L}}{\mathrm{R}} \frac{1}{\mathrm{e}}\)

\(=\frac{\varepsilon \mathrm{L}}{\mathrm{e} \mathrm{R}^{2}}\)