Two solid spheres, 1 and 2, of density 1.0 g/cm3 and 10.0 g/cm3 , respectively, are in an inert liquid medium 3 of density 2.0 g/cm3 and dielectric constant 2.0. Sphere 1 carries a charge e, and sphere 2 carries a charge -e. If the spheres have the same radius R, calculate the value of R for there to be no longrange force between them at any separation D.