Normal incidence means that the incident sound beam strikes the boundary at _____.

Normal incidence means that the incident sound beam strikes the boundary at _____.

• A. Exactly 90 degrees
• B. Less than 90 degrees
• C. Greater than 90 degrees
• D. 0 degrees

Answer: (A)

Normal incidence occurs when the sound beam strikes the boundary straight on, at a right angle to the surface. When the beam meets the boundary this way, it passes through without bending (no refraction) and the transmitted wave continues directly forward. Any energy that reflects does so because of impedance differences between the two media, but the direction of the incoming and reflected waves remains aligned along the same line. The other angles describe oblique approaches, where the wave can refract and change direction at the boundary.

Normal incidence occurs when the sound beam strikes the boundary straight on, at a right angle to the surface. When the beam meets the boundary this way, it passes through without bending (no refraction) and the transmitted wave continues directly forward. Any energy that reflects does so because of impedance differences between the two media, but the direction of the incoming and reflected waves remains aligned along the same line. The other angles describe oblique approaches, where the wave can refract and change direction at the boundary.