Question

In the Millikan oil droplet experiment, the oil is sprayed from an atomizer into a chamber. The droplets are allowed to pass through the hole into the chamber so that their fall can be observed. The top and bottom of the chamber consist of electrically charged plates. The upper plate is positively charged, and the lower plate is negatively charged. X rays are introduced into the chamber so that when they strike the oil droplets, the droplets will acquire one or more negative charges. The electric field (voltage) is applied to the metal plates.

Watch the animation and identify the effects of an electric field on the motion of a negatively charged oil droplet. Consider the gravitational force as Fg and the electric force as Fe. All the other forces acting on the oil droplet can be ignored as their effect on the motion of the oil droplet is negligible.

A/ In the absence of an electric field, the oil droplet falls freely due to the gravitational force.

B/ If Fe is increased until it is equal to Fg, the negatively charged oil droplet will remain stationary.

C/ If Fe is greater than Fg, the negatively charged oil droplet will move freely toward the negatively charged plate.

D/ In the presence of an electric field, the negatively charged oil droplet moves freely toward the negatively charged plate.

** I chose B, but that was the wrong answer