Experience shows that a body irradiated with light with circular polarization acquires a torque. This happens because such a light possesses an angular momentum whose flow density in vacuum is equal to M = I/w), where I is the intensity of light, w is the angular oscillation frequency. Suppose light with circular polarization and wavelength λ = 0.70 Dm falls normally on a uniform black disc of mass m = l0 mg which can freely rotate about its axis. How soon will its angular velocity become equal to wo = 1.0 rad/s provided I = 10 W/cm2?