When sound waves encounter a boundary between different media, such as from air to a solid surface or from one solid material to another, several things can happen, including reflection, transmission, and absorption.
Reflection occurs when sound waves encounter a boundary and bounce back into the original medium. This happens because the boundary acts as a barrier to the sound waves, causing them to change direction. The angle at which the sound waves reflect depends on the angle of incidence and the properties of the boundary material.
Transmission occurs when sound waves pass through the boundary and continue propagating into the new medium. Whether sound can penetrate inside the new medium depends on factors such as the properties of the medium, the frequency of the sound waves, and the angle of incidence.
Absorption happens when sound waves are absorbed by the material at the boundary. The energy of the sound waves is converted into other forms, such as heat, within the absorbing material.
The behavior of sound waves at a boundary depends on the impedance mismatch between the two media. Impedance is a measure of how difficult it is for sound waves to travel through a medium. When the impedance mismatch is significant, such as between air and a solid, a large portion of the sound energy can be reflected. This is because the properties of the two media, such as their densities and elasticities, are different.
Additionally, the wavelength of sound waves plays a role. If the wavelength is comparable to the size of the boundary features or the atomic/molecular structure of the medium, scattering and reflection can occur. This can prevent the sound waves from penetrating deeper into the medium.
In summary, when sound waves encounter a boundary, they can be reflected, transmitted, or absorbed, depending on factors such as the impedance mismatch, the angle of incidence, the frequency of the sound waves, and the properties of the materials involved. The extent to which sound penetrates inside a medium depends on these factors and the specific characteristics of the boundary and the medium.