Question

Sound waves of frequency 320 Hz are sent into the top of a vertical tube containing water at a level that can be adjusted.If standing waves are produced at two successive water levels of 20 cm and 73 cm from the bottom, the speed of sound waves in the air of tube is :

• A. 320 m$s^{-1}$
• B. 339 m$s^{-1}$
• C. 350 m$s^{-1}$
• D. 369 m$s^{-1}$

Answer 1

Answer: (B)

339 m$s^{-1}$

Through figure we can see that distance between water levels is equal to the distance between successive nodes or half of a wavelength.
$\frac{\lambda }{2}=73-20=53\Rightarrow \lambda =106cm=1.06m\Rightarrow v=f\lambda =320\times 1.06=339m/s$