(a) In self inductance, the change in the strength of current in the coil is opposed by the coil itself by inducing an e.m.f. In mutual inductance, a pair of coils are involved. If current changes in one coil, the other near by coil opposes the change by inducing an e.m.f. in itself. (b) Induced emf $=\left|e\right| = M\; \frac{dI}{dt} = 2 \times \; \frac{0.5}{100 \times 10^{-3}} =5\,\mathrm{V}$ $\;\; \text{Induced emf}\;=\left|e\right|=\; \frac{d\phi}{dt}$ $\; \;\;\;\; 5=\; \frac{d\phi}{100 \times 10^{-3}}$ $\; d\phi=\; \text{change in flux}\;$ $=5 \times 100 \times 10^{-3} = 0.5\,\mathrm{Wb}$