What Is the Mass of an Oil Drop Balanced Between Metal Plates?

[atomicpedals]

Homework Statement

Two horizontal metal plates are 1cm apart in air. An oil drop bearing a charge of one electronic unit is balanced between the plates when the potential difference between them is 800volts. Find the mass of the drop.

Homework Equations

I may need to use some combination of: dV = -E ds, and W = 1/2 eE^2l. But I'm really not even very certain on that.

The Attempt at a Solution

Really I've got nothing on this one! Any suggestions of which way to look for the solution would be much appreciated.

 

[ideasrule]

What's the electric field between the plates of a parallel-plate capacitor? Once you get that, write out the equilibrium condition between the electric and gravitational forces.

 

[atomicpedals]

Ok, so we have that E=V/d and then that EQ=mg (equilibrium condition), this will then yield Q=dmg/V.

I think I'm playing the right ball-game now, but this seems too simple (and doesn't yield a result that makes sense assuming my arithmetic is correct). Should my final condition take the characteristics of air into consideration?