OR (b) (i) A rectangular coil of N turns and area of cross-section A is rotated at a steady angular speed $\omega$ in a uniform magnetic field. Obtain an expression for the emf induced in the coil at any instant of time. (ii) Two coplanar and concentric circular loops $L_1$ and $L_2$ are placed coaxially with their centres coinciding. The radii of $L_1$ and $L_2$ are 1 cm and 100 cm respectively. Calculate the mutual inductance of the loops. (Take $\pi^2 = 10$)