A charged oil droplet falls 4 mm in 18.0 s at terminal speed in the absence of an electric field. The specfic gravity of air is 1.35 multiplied by 10-3, and that of the oil is 0.75. The viscosity of air is 1.80 multiplied by 10-5 (N·s)/m2.
(a) What is the radius of the drop?
(b) What is the mass of the drop?
(c) If the droplet carries 2 units of electric charge and is in an electric field of 2.5 multiplied by 105 V/m. what is the ratio of the electric force to the gravitational force on the droplet?