Approximately what percentage of the sound beam reflects from a media boundary with perpendicular incidence, when the impedances are different?

When sound waves pass from one medium to another and encounter a boundary, the amount of sound energy reflected at that boundary depends on the acoustic impedance of the two media. Impedance is a measure of how much resistance a medium provides to the flow of sound waves. The greater the difference in impedance between the two media, the higher the percentage of sound energy that will be reflected.

For perpendicular incidence, the reflection coefficient can be calculated using the formula:

[ R = \frac{Z_2 - Z_1}{Z_2 + Z_1} ]

where ( Z_1 ) is the impedance of the first medium and ( Z_2 ) is the impedance of the second medium. If the impedance difference is relatively small, typically around 0.5 to 1.0 when comparing soft tissues or fluids, the reflection is minimal.

Thus, if the impedances between two media are only slightly different, around 1% of the sound beam would reflect off this boundary, which aligns closely with the first choice presented. This understanding highlights that a small degree of reflection occurs when the two media are closely matched in terms of acoustic impedance.

As the differences in impedance increase, the reflection percentage would rise significantly, for