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.
An electric eld is established by applying a potential difference to the plates. It is found that a eld of strength E0 willcause the droplet to be suspended motionless. Write an expression for the droplet’s charge in terms of the suspending field E0 and the droplet’s weight mg.