ARDMS Sonography Principles And Instrumentation (SPI) Practice Exam

When a sound wave encounters a boundary between two media, the degree to which the wave is refracted depends on the acoustic impedances of the media involved. Acoustic impedance is determined by the density of the medium and the speed of sound within that medium. If the impedances of two media are identical, the characteristic of the boundary changes significantly. When sound travels at normal incidence – meaning it strikes the boundary directly at a 90-degree angle – the wave behavior is defined by the relationship between the impedances of the two media. If the impedances are identical, this means that the wave experiences no change in speed or direction as it crosses the boundary. Since there is no impedance mismatch, the sound wave does not experience refraction; instead, it transmits unchanged into the second medium. In practical terms, this means that 100% of the sound wave continues into the second medium, but the concept of refraction does not apply in this case, leading to 0% refraction. Therefore, when the impedances are the same, the expectation is that the entire wave is transmitted into the second medium without any refracted portion, validating the selection of zero percent for the refracted component.