Material interface

A wave carries energy towards a material interface: the boundary where two materials meet, such as air and glass or air and a wall. At that boundary, the wave need not have just one outcome. Some of its energy may return, some may pass into the second material, and some may be taken up by the material.

A material interface is the boundary between two materials, such as air and glass. When a wave reaches an interface, its energy need not follow a single path. Some of the wave may be transmitted into or through the new material, while some may be absorbed or redirected at the boundary.