Echoes and Sound Wave Reflection

Steps:

• Define an echo as a repeated sound heard after a delay.
• Explain that echoes occur when sound waves bounce back from a surface.
• Compare to choices: identify reflection as the bouncing process.
• Eliminate unrelated wave behaviors like bending or converging.

Why B is correct:

• Echoes form via the reflection of sound waves, where waves rebound off hard surfaces following the law of reflection (angle of incidence equals angle of reflection).

Why the others are wrong:

• A: Focusing converges waves to a point, as in lenses, not echoing.
• C: Refraction bends waves passing between media, changing speed and direction, unrelated to bouncing back.
• D: Total internal reflection is a specific reflection type at critical angles in optics, not the general process for echoes.

Final answer: B