Figure $P 25.16$ shows a 100 -turn coil of wire of radius $12 \mathrm{cm}$ in a $0.15 \mathrm{T}$ magnetic field. The coil is rotated $90^{\circ}$ in $0.30 \mathrm{s}$, ending up parallel to the field. What is the average emf induced in the coil as it rotates?