Electromagnetic Induction

A wheel of 20 metallic spokes each 40 cm long is rotated with a speed of $180 \mathrm{rev} / \mathrm{min}$ in a plane normal to the horizontal component of earth's magnetic field $H_c$ at a place. If $H_c=0.4 \mathrm{G}$ (Gauss) at that place, the induced emf between the axle and the rim of the wheel is