Sometimes we are concerned with what happens when a wave in one medium encounters a sharp boundary with a second medium. If the properties of the second medium are similar to those of the first medium, the wave passes from the first medium to the second, or is transmitted (see figure).
If the properties of the second medium are markedly different from the first, there is said to be an impedance mismatch, and much of the wave energy is reflected (see figure), while some is transmitted.
The situation is slightly more complicated if the boundary between the two media is gradual. In this case most of the energy of a wave may be transmitted to the second medium even if there is an impedance mismatch. This occurs if the length of the transition region is large compared with the wavelength of the wave (see figure). If not, then the wave "sees" the boundary as being sharp.
In addition to being reflected and transmitted, sometimes wave energy is absorbed. Certain media convert wave energy into heat energy. This can happen, for instance, for a wave traveling along a rope. The rope fibers rub against each other and the energy dissipates as heat (see figure).
For the following questions, refer to the following chart, which shows the typical wavelengths of various waves.
wave typical wavelength
ocean wave 10–100 m
swimming pool wave 0.1 m
sound wave 1 m
visible light 10–7 m
When sound waves encounter a closed door, what is most likely to happen?