In this thesis an attempt is made to study the effects of magnetic field on some flows in channels and past infinite plates. In chapter 1 the effect of small uniform magnetic field on separation of a binary mixture for the case of fully developed natural convection of a fluid between two heated inclined plates is investigated.In chapter 2 free and forced convection flow of viscous incompressible fluid in a horizontal wavy channel has been studied. In chapter 3 Hall current effects on unsteady flow of viscous, incompressible fluid between two horizontal parallel non conducting plates, are...