$A$ student performed an experiment to measure the speed of sound in air using the resonance air-column method. Two resonances in the air-column were obtained by lowering the water level. The resonance with the shorter air-column is the first resonance and that with the longer air-column is the second resonance. Then,

Two closed organ pipes having lengths $20\,cm$ and $20.5\,cm$ produce $5\,beats/sec$. Determine the frequency of both organ pipes.

An air column is of length $17 \ cm$. The ratio of frequencies of the $5^{\text{th}}$ overtone for an air column closed at one end to that open at both ends is (velocity of sound in air $= 340 \ ms^{-1}$).

The fundamental frequency of an air column in a pipe open at both ends is $f_1$. Now $80\%$ of its length is immersed in water,the fundamental frequency of the air column becomes $f_2$. The ratio of $f_1:f_2$ is

Two open organ pipes of fundamental frequencies $n_1$ and $n_2$ are joined in series. The fundamental frequency of the new pipe so obtained will be

$A$ person blows into the open end of a long pipe. As a result,a high-pressure pulse of air travels down the pipe. When this pulse reaches the other end of the pipe,which of the following statements are true?
$(I)$ $A$ high-pressure pulse starts travelling up the pipe,if the other end of the pipe is open.
$(II)$ $A$ low-pressure pulse starts travelling up the pipe,if the other end of the pipe is open.
$(III)$ $A$ low-pressure pulse starts travelling up the pipe,if the other end of the pipe is closed.
$(IV)$ $A$ high-pressure pulse starts travelling up the pipe,if the other end of the pipe is closed.