# Two identical spherical water drops are picking up one monovalent ion.What weight has to have each drop so that theĀ gravitational force to balance coulomb rejection force?

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We'll use Newton's law,so we'll make an equality between the gravitational force and rejection force:

gama* m^2/r^2=e^2/4*pi*epsilon0*r^2

From this equality, we'll extract the weight:

m=e/ sqrt (4*pi*epsilon0*gama)=1.8ng