Two identical charged balls, suspended on threads of equal length, are lowered into kerosene. What should be the density p of the material of the balls so that the angle of divergence of the threads in air and in kerosene is the same? Kerosene density pk = 0.8 g/cm3, relative dielectric constant e = 2. (And henceforth e means the relative dielectric constant of the dielectric. The absolute permittivity is equal to eо, where eо = (1/36) 10-9 f/m - dielectric vacuum permeability.)

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