The law that the frequency of luminescence induced by radiation is usually less than the frequency of the radiation.The force acting downward is equal to 4/3πr3 (d1 - d2)g, in which d1 is the density of the sphere, d2 is the density of the liquid.
                                            At a constant velocity of fall velocityis expressed by Stokes’s law as v = 2/9(d1 - d2)gr2/η.

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