Echo is produced by reflection of sound waves from a denser medium. What is the phase change between sound wave and echo?
Correct answer: B. 180 degrees
- A. 0 degrees
- B. 180 degrees
- C. 270 degrees
- D. 90 degrees
Explanation
When a sound wave is reflected from a denser medium, the reflected wave undergoes a phase change of 180 degrees or pi radians. This is because the denser medium causes the wave to undergo a reflection with a fixed boundary condition, and at the fixed boundary, the displacement of the particles of the medium is inverted while the pressure remains constant. This results in a phase shift of 180 degrees. So, when the reflected wave superimposes with the incident wave, they are out of phase by 180 degrees, leading to the formation of an echo.
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