An ultraviolet wave of continuous frequency reflects from a solid surface back in the direction of the transmitter. Assuming no amplitude is lost, describe and explain the behaviour of the particles in the medium between the transmitter and surface.

The transmitted and reflected waves are of equal frequency and are both continuous, so they will superpose and interfere with each other. In the regions of maximal constructive interference, antinodes will form where the particles have maximum amplitude, equal to double the amplitude of the initial wave. In regions of maximum destructive interference, nodes will form which have an amplitude of zero: the particles in this region will not move. This is a standing wave.