1. Millikan used Stokes's law, which says that a small sphere of radius a falling with velocity v in a homogeneous medium of viscosity n = 18.6 x10 Pa s is subject to a retarding force F = 6xnav. He observed that a drop of oil of density p = 0.92g cm would fall 0.522cm in 13.6s. a. What was the radius of the drop? b. What was its mass