Question

The phase change between incident and reflected sound wave from a fixed wall is

• A. 0
• B. $\pi$
• C. $3\pi$
• D. $2\pi$

Answer 1

Answer: (B)

When a wave is reflected from a wall, the wave is inverted.
As the phase difference between a wave and its inverted wave is $\bar{n}$, the phase difference is $\pi$
$y=A\cos (kx+\omega t)$
$y_r=-A\cos (kx+\omega t)$
$=A\cos (kx+\omega t+\pi )$
$\Rightarrow \varphi =\pi$