//chapter10,Example10_10,pg 275

//F=mg=qE

E=250

R=10^-8

rho=10^3//density

m=(4/3)*%pi*(R^3)*rho//m=volume*density

W=m*9.8//weight of drop(mg)

q=W/E

printf("charge on water drop\n")

disp(q)