How Is the Charge on a Suspended Oil Drop Determined in Millikan's Experiment?

[spottedcow913]

In Milikan's experiment, an oil drop of radius 1.64x10^-6 m and density of 0.851 g/cm^3 is suspended in a chamber where the downward electric field of 1.92x10^5 N/C is applied. Find the charge on the on drop.

I know that F=qE, but the drop is suspended so it can't really a force because it has no acceleration. I also know I can find a mass from the info, but, again that doesn't help my force because the drop is suspended. Should I try to use the idea of an electric field due to a point charge?

Thanks for any help!

 

[gneill]

If the drop is suspended (not accelerating) that means that the forces are balanced (net force is zero).