question_answer 25)

An oil drop of 12 excess electrons is held stationary under a constant electric field of in Millikan's oil drop experiment. The density of the oil is . Estimate the radius of the drop.  

Answer:

Charge on drop,                                                 Electrical force on drop,                                                 Weight of the drop,                                 i.e.,                 For equilibrium,                 i.e.,                                 or                 or.