Reflected and Transmitted waves at two different boundaries:
When a wave comes across a change in the medium, an interface surface, a portion of the wave's energy is reflected back, and another portion is transmitted through the boundary.
Reflected and transmitted waves are generated by the incident wave. The reflected and transmitted waves do not depend exclusively on the incident wave and its angle of incidence, but also on the properties of the medium behind the interface surface.
If the amplitude of the reflected wave is equal to that of the incident wave. Thus, the intensity in both waves is equal; no losses occur at the boundary. Second, because δ = π, the reflected wave is phase shifted 180° with respect to the incident wave.
At a free (soft) boundary, the restoring force is zero and the reflected wave has the same polarity (no phase change) as the incident wave. When a wave encounters a boundary which is neither rigid (hard) nor free (soft) but instead somewhere in between, part of the wave is reflected from the boundary and part of the wave is transmitted across the boundary. If the transmission of a wave is from Less to more dense medium, then the reflected wave will be inverted in this case. If the transmission of a wave is from more to less dense medium, then the reflected wave will be non–inverted in this case.