Consider an oil droplet of mass m and charge q. We want to determine the charge on the droplet in a Millikan-type experiment. We will do this in several steps. Assume, for simplicity, that the charge is positive and that the electric field between the plates points upward. (c) A spherical object of radius r moving slowly through the air is known to experience a retarding force Fₔᵣₐ₉ = −6πηrv where η is the viscosity of the air. Use this and your answer to part b to show that a spherical droplet of density ρ falling with a terminal velocity vₜₑᵣₘ has a radius . r = √9ηvₜₑᵣₘ / 2pg