The elementary effect of induced transition interaction of a moving charge crossing the boundary between two dielectric half-spaces with the field of a monochromatic wave scattered at this boundary is studied. The quantitative relation between this effect and the corresponding collective process of excitation of charge density waves at the same nonuniformity, i. e., the modulation of the flux of charged particles by the field of a counter-propagating wave, is found. The contribution of the physical phenomena under investigation to the development of beam instabilities and electromagnetic wave generation is discussed.