OR (b) (i) State Lenz's law and explain that it follows the law of conservation of energy. (ii) Write the dimensional formula for self-inductance. The current in a coil changes from $8\cdot0\ \text{A}$ to $2\cdot0\ \text{A}$ in $0\cdot6\ \text{s}$. If an average emf induced in the coil is $50\ \text{V}$, calculate the self-inductance of the coil.