What two conditions must be present to cause refraction of a sound wave?

What two conditions must be present to cause refraction of a sound wave?

• A. Perpendicular incidence and identical media propagation speeds.
• B. Oblique incidence and different media propagation speeds.
• C. Perpendicular incidence and reflector size smaller than one wavelength.
• D. Oblique incidence and reflector size smaller than one wavelength.

Answer: (B)

Refraction occurs when a sound wave crosses into another medium at an angle and the two media have different propagation speeds. When the incidence is oblique, different parts of the wavefront enter the new medium at different times, so the wave changes direction as it passes the boundary. If the incidence is perpendicular to the boundary, the wavefront crosses uniformly and there’s no bending, even if the speeds differ. The size of a reflector or boundary doesn’t drive refraction; it affects other phenomena like scattering. So the two conditions needed are hitting the boundary at an angle and having different sound speeds in the two media.

Refraction occurs when a sound wave crosses into another medium at an angle and the two media have different propagation speeds. When the incidence is oblique, different parts of the wavefront enter the new medium at different times, so the wave changes direction as it passes the boundary. If the incidence is perpendicular to the boundary, the wavefront crosses uniformly and there’s no bending, even if the speeds differ. The size of a reflector or boundary doesn’t drive refraction; it affects other phenomena like scattering. So the two conditions needed are hitting the boundary at an angle and having different sound speeds in the two media.