The same formula is used to determine

• A. Angular relationships
• B. Phase velocities
• C. Amount of reflected sound energy
• D. Acoustic impedance

Answer: (A)

The thing being tested is how the angle of a ultrasonic beam changes when it crosses an interface, which is described by Snell’s law. In this context, the relationship is written as sin(angle in first medium) divided by the velocity in the first medium equals sin(angle in second medium) divided by the velocity in the second medium. This means you can determine how the beam will bend (the angular relationship) if you know the incident angle and the two phase velocities, or you can compare angles to infer the velocity ratio. Because this equation directly governs the bending of the beam at interfaces, it’s the tool used to determine angular relationships.

Phase velocities themselves are properties of the media, not something you solve for from the angles alone. The amount of reflected sound energy depends mainly on the impedance mismatch between the media, not on the angle relationship described by Snell’s law. Acoustic impedance is a separate property (mass density times speed) and is not determined by the angle relation.