The second critical angle is defined as the longitudinal incident angle that results in what for the refracted transverse wave?

• A. A Refracted Transverse Wave of Ninety Degrees
• B. A Reflected Transverse Wave
• C. A Refracted Longitudinal Wave
• D. No Refraction Occurs

Answer: (A)

The main idea here is that a longitudinal incident wave can generate a shear (transverse) wave as it meets a boundary between media. The second critical angle is the specific incident angle at which the refracted transverse (shear) wave travels along the boundary, i.e., it is at 90 degrees to the normal. That’s why the correct description is a refracted transverse wave at ninety degrees—the shear wave is being refracted so it moves parallel to the surface.

In practical terms, this angle marks the limit where the transverse wave stops propagating away from the interface into the second medium and instead travels along the boundary. The other options don’t describe this boundary-then-surface-travel situation: you’re not at a condition where a reflected transverse wave is the defining feature, nor is it a refracted longitudinal wave at that particular angle, nor is it the absence of any refraction.