Question

A wave travelling along positive $ x- $ axis is given by $ y=A\sin (\omega t-kx). $ If it is reflected from a rigid boundary such that 80% amplitude is reflected, then equation of reflected wave is

• A. $ y=A\sin (\omega t+0.8kx) $
• B. $ y=-0.8A\sin (\omega t+kx) $
• C. $ y=A\sin (\omega t+kx) $
• D. $ y=0.8A\sin (\omega t+kx) $

Answer 1

Answer: (B)

On getting reflected from a rigid boundary the wave suffers. Hence, if
$ {{y}_{incident}}=A\sin (\omega t-kx) $
Then, $ {{y}_{reflected}}=(0.8A)\sin \{\omega t-k(-x)+\pi \} $
$ =-0.8A\sin (\omega t+kx) $
an additional phase change of $ \pi . $