Question: Millikan used Stokes's law, which says that a small sphere of radius a falling with velocity v in a homogeneous medium of viscosity η = 18.6× 10-6 Pas is subject to a retarding force F = 6πηav.
He observed that a drop of oil of density ρ = 0.92gcm-3 would fall 0.522cm in 13.6s.
a. What was the radius of the drop?
b. What was its mass?