What happens to the charged oil droplet in Milikan's experiment?

In Millikan's experiment, the charged oil droplets are manipulated using an electric field to balance the forces acting on them. Initially, the droplets can either rise or fall due to the effects of gravity and the electric force applied. When the electric field strength is increased, it exerts a force on the charged droplets in the opposite direction of gravitational force.

The key point about choice C is that when the electric field strength is precisely adjusted to match the gravitational force acting on the droplet, the droplet will remain stationary in equilibrium. This state of balance allows Millikan to determine the charge of the oil droplet by measuring the electric field strength necessary to hold the droplet in place, giving insights into the nature of electric charge quantization.

Thus, the correct response reflects the principle of equilibrium achieved in this iconic experiment, where the droplet is suspended in mid-air and does not move when these opposing forces are equal.