We show that in a dusty plasma consisting of a plasma (density n and temperature T) and dust grains (density N and radius a) the charge on a grain is not given by its free-space value Qo = Va, where V is its surface potential. Instead the charge is reduced by a factor 1 + x, with x = 4πNaλD², where λD is the plasma Debye length. Except in the optically thin E and G rings this factor is large. Usually electromagnetic forces on dust particles in Saturn's ring system are too small to produce observable effects. The current carried by dust particles moving relative to the plasma with a speed w is to a good approximation given by j = NQw. Thus magnetic perturbations by the F ring should be much smaller than previously estimated.