An analytical theory of the RF-field distribution in a warm homogeneous magnetized plasma slab or plasma cylinder, with electron reflecting boundaries, is developed. Simple solutions of the Boltzmann equation coupled to the Maxwell equations are found, in case the effective penetration depth of the RF-field excited at the boundary of the plasma cylinder is small compared to the cylinder radius. These solutions satisfactorily describe experimental results obtained for cylindrical Ar-plasmas in an axial magnetic field. A possibility of the existence of the Azbel-kaner cyclotron-resonance in this model is discussed.