Question

An open pipe is in resonance in its fundamental mode. Air, hydrogen, ethane are filled in succession in this pipe. The velocity of sound is different in these three media on account of which

• A. Both frequency and wavelength change
• B. Only the frequency changes
• C. Amplitude change
• D. Only the wavelength changes

Answer 1

Answer: (B)

We know, $V=f\lambda$, where $V$ = speed of sound; $f$ = frequency and $\lambda$ = wavelength
The resonance is a standing wave phenomenon in the air column and occurs when the column length is $\lambda$/2, $\lambda$, 3$\lambda$/2 ... ( in case of open pipe)
So in resonance condition amplitude and wavelength cannot change.
Only frequency changes for different kind of gases.