Question

If the velocity sound in air is 336 m/s, the maximum length of a closed pipe that would produce a just audible sound is-

• A. 4.2 m
• B. $4.2\times {10}^{-2}m$
• C. 1 m
• D. $4.2\times {10}^{-3}m$

Answer 1

The correct option is A 4.2 m

Velocity of sound in air $v=336$ m/sec
We know that the lowest frequency of audible sound is $20$ Hz. Hence, maximum length of a closed pipe to produce just audible sound in given by Fundamental frequency
${\lambda }_{max}\Rightarrow f_{reg}$ minimum $=20$ Hz
$\Rightarrow 20=\frac{v}{4l}\Rightarrow l=\frac{336}{4\times 20}$
$l=4.2m$