Question

The phase difference between two points separated by $0.8m$ in a wave of frequency $120Hz$ is ${90}^{}$. Then the velocity of wave will be

• A. $192m/s$
• B. $360m/s$
• C. $710m/s$
• D. $384m/s$

Answer 1

The correct option is D $384m/s$

$\Delta \varphi ={90}^{\circ }=\frac{a}{2}$

$\Delta x=0.8m$

we know that $\Delta \varphi =\frac{2\pi }{\alpha }\times \Delta x$

So $\lambda =\frac{2\pi \times \Delta x}{\Delta \varphi }=\frac{2\pi \times 0.8}{\pi /2}$

$\Rightarrow \lambda =3.2m$

$v=120Hz$ & $v=v\lambda$

$velocityv=120\times 3.2=384m/s$