If we study the vibration of a pipe open at both ends,then the following statement is not true.

In an experiment to determine the velocity of sound in air at room temperature using a resonance tube,the first resonance is observed when the air column has a length of $20.0 \,cm$ for a tuning fork of frequency $400 \,Hz$. The velocity of sound at room temperature is $336 \,ms^{-1}$. The third resonance is observed when the air column has a length of ......... $cm$.

$A$ glass tube of $1 \,m$ length is filled with water. The water can be drained out slowly from the bottom of the tube. If a vibrating tuning fork of frequency $500 \,Hz$ is brought at the upper end of the tube, then the total number of resonances obtained are [Velocity of sound in air is $320 \,m/s$].

Two open organ pipes of fundamental frequencies $n_{1}$ and $n_{2}$ are joined in series. The fundamental frequency of the new pipe is

If the seventh harmonic of a closed organ pipe is in unison with the fourth harmonic of an open organ pipe, then the ratio of the length of the closed pipe to that of the open pipe is:

At a temperature of $27^{\circ} C$, two identical organ pipes produce notes of frequency $140 \,Hz$. If the temperature of one pipe is raised to $57.75^{\circ} C$, then the number of beats produced per second is