The self induced emf of a coil is 25 volts.

(2) According to faraday's law of electromagnetic induc-

tion, $\mathrm{e}=\frac{-\mathrm{d} \phi}{\mathrm{dt}}$

$\mathrm{L} \times \frac{\mathrm{di}}{\mathrm{dt}}=25 \Rightarrow \mathrm{L} \times \frac{15}{1}=25$

or, $\mathrm{L}=\frac{5}{3} \mathrm{H}$

Change in the energy of the inductance,

$\Delta \mathrm{E}=\frac{1}{2} \mathrm{~L}\left(\mathrm{i}_{1}^{2}-\mathrm{i}_{2}^{2}\right)=\frac{1}{2} \times \frac{5}{3} \times\left(25^{2}-10^{2}\right)$

$=\frac{5}{6} \times 525=437.5 \mathrm{~J}$