Question

The phase difference between two points separated by $0.8\, m$ in a wave of frequency $120\, Hz$ is $0.5 \pi$. The wave velocity is

• A. $144\, ms ^{-1}$
• B. $384\, ms ^{-1}$
• C. $256\, ms ^{-1}$
• D. $720\, ms ^{-1}$

Answer 1

Answer: (B)

Here, $n=120\, Hz$,
$x=0.8\, m , \phi=0.5 \pi$
From $\phi=\frac{2 \pi}{\lambda} x, $
$\lambda=\frac{2 \pi x}{\phi}=\frac{2 \pi \times 0.8}{0.5 \pi}=3.2\, m$
$\Rightarrow v =n \lambda=120 \times 3.2=384\, ms ^{-1}$