We show that in a dusty plasma consisting of a plasma (density n and temperture T) and dust grains (density N and radius a) the charge on a grain is not given by its free-space value Q0=Va, where V is its surface potential. Instead the charge is reduced by a factor 1+x, with x=4&pgr;Na&lgr;D2, where &lgr;D is the plasma Debye length. Except in the optically thin E and G rings this factor is large. Usually electromagnetic forces on dust particles on Saturn's ring systems are too small to produce observable effects. The current carried out dust particles moving relative to the plasma with a speed w is to a good approximation given by j=NOw. Thus magnetic perturbations by the F ring should be much smaller than previously estimated.