The change in direction when an ultrasonic wave passes from a medium of one velocity into a medium with a different velocity is called?

• A. Refraction
• B. Rarefaction
• C. Angulation
• D. Reflection

Answer: (A)

Refraction occurs when an ultrasonic wave crosses a boundary into a medium with a different propagation speed, causing its path to bend. The change in velocity means the transmitted angle must satisfy Snell’s law, sin(theta_in)/v_in = sin(theta_trans)/v_out. If the second medium is slower, the ray bends toward the normal; if faster, it bends away from the normal. Rarefaction is just part of the wave cycle, and reflection is the wave bouncing back from the boundary, not the bending of the transmitted path.