Suppression of backscattering. Only a small fraction of the electrons injected by the current source into the 2DEG is transmitted through the point contact. The remaining electrons are scattered back into the source contact. This is the origin of the nonzero resistance of a ballistic point contact. In this subsection we shall discuss how a relatively weak magnetic field leads to a suppression of the geometrical backscattering caused by the finite width of the point contact, while the amount of backscattering caused by the potential barrier in the point contact remains essentially unaffected.