In a Millikan’s oil drop experiment, a drop is observed to fall with a terminal speed 1.4 mm/s in the absence of electric field. When a vertical electric field of 4.9x105
V/m is applied, the droplet is observed to continue to move downward at a lower
speed 1.21 mm/s. Calculate the charge on the drop. ( Density of oil = 750 kg/m3
,
viscosity of air = 1.81x 10 -5 kg/ms and density of air = 1.29 kg/m3
)