Question

A 0.7 um-diameter droplet of oil, having a charge of +e, is suspended in midair between two horizontal plates of a parallel-plate capacitor. The upward electric force on the droplet is exactly balanced by the downward force of gravity. The oil has a density of 860 (kg/m^3), and the capacitor plates are 5.0 mm apart. What must the potential difference be to hold the droplet in equilibrium?