d
\(<\varepsilon>=\frac{\int \varepsilon dt }{\int dt }=\frac{\int( Ldi / dt ) dt }{\int dt }=\frac{ L \int di }{\int dt }\)

\(<\varepsilon>=\frac{ L \Delta i }{\Delta i }\)

\(i _{0}=\frac{ V }{ R }=\frac{20}{10}=2 \; A , \text { if } i =0 \; A\)

\(T =100 \; \mu s , L =20 \; mH\)

\(< \varepsilon>=\frac{20 \times 10^{-3} \times(2-0)}{100 \times 10^{-6}}.\)

\(=\frac{2 \times 10^{3}}{5}\)

\(< \varepsilon > =400 \; V\)