Module 2 : Electrostatics
Lecture 6 : Quantization Of Charge
 

where $a$is the radius of the droplet. You can detrmine the terminal velocity by observing the time of fall of the droplet. If density of oil is $\rho$, the mass $M= 4\pi a^3\rho/3$. Using these, mass and the radius of the drop can be detrmined :

$\displaystyle{ a= \sqrt{\frac{9\eta v_0}{2g\rho}}}$
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