Question

Air is blown at the mouth of a tube of length 25 cm and diameter equal to 2 cm open at both ends. If velocity of sound in air is 330 ms${}^{-1}$ the sound emitted will have all the frequencies in the group (neglect end correction)

• A. 330, 990, 1690 Hz
• B. 302, 664, 1320 Hz
• C. 660, 1320, 1980 Hz
• D. 660, 1000, 3300 Hz

Answer 1

Answer: (C)

660, 1320, 1980 Hz

As it is open at both ends, antinodes are formed at both ends

$\Rightarrow lengthl=n\left(\frac{\lambda }{2}\right)\Rightarrow \lambda =\frac{2l}{n}$

Velocity $v=f\lambda$

$\Rightarrow f=\frac{v}{\lambda }=\left(\frac{v}{2l}\right)n.$

$=(\frac{330}{2\times 25\times {10}^{-2}}{)}^n$

$=n\left(660\right)$