Question

The pitch of an organ pipe is highest when the pipe is filled with

• A. Air
• B. Hydrogen
• C. Oxygen
• D. Carbon dioxide

Answer 1

Answer: (B)

$v=f\lambda$
$=\lambda$ is constant for an organ pipe
$v=\sqrt{\frac{\gamma RT}{M}}$
$=\frac{1}{\sqrt{M}}$
$v$ is maximum when $M$ is least.
Thus, velocity of sound in air is maximum when $M$ is least.
Since $f\propto v$ so $f\propto \frac{1}{\sqrt{M}}$
Hence, frequency is maximum when $M$ is least.
Hence, among options answer is $H_2$