Paleomagnetic research indicates that the strength of the earth dipole varies over the range 0.1 to 3.0 of the present value. Consequences for magnetospheric physics of changes in the strength of the magnetic dipole are explored in this paper. The changes in the sizes of the magnetosphere and plasmasphere due to variations in dipole strength and to variations in solar wind parameters at a given dipole strength are given. The plasmasphere size varies more slowly with dipole strength than the magnetosphere size over the range considered. Thus the plasmasphere occupies a relatively larger fraction of the magnetosphere for small dipole strengths. The plasmasphere frequently extends beyond synchronous orbit for dipole strengths greater than twice the present value. For a given solar wind condition the power into the magnetosphere and the brightness of auroras increase for larger dipole strengths. However, for smaller dipole strengths, auroras are seen at lower latitudes and over a greater range of latitudes. Magnetic storms are stronger and more frequent for smaller dipole strengths.