Question

The length of a sonometer wire is $90cm$ and the stationary wave setup in the wire is represented by an equation: $y=6sm\left(\frac{\pi x}{30}\right)\cos \left(250t\right)$ where $x$, $y$ are in cm and $t$ is in second. The number of loops is

• A. $1$
• B. $2$
• C. $4$
• D. $3$

Answer 1

The correct option is D $3$

$\frac{2\pi }{\lambda }=\frac{\pi }{30}$
$\lambda =60cm$
$\frac{\lambda }{2}=30cm$
$\therefore 3$ loops are formed as $3\left(30\right)=90cm.$