Question

A resonance air column of length $20\, cm$ resonates with a tuning fork of frequency $450\, Hz$. Ignoring the correction, the velocity of sound in air will be

• A. 920 m/s
• B. 720 m/s
• C. 820 m/s
• D. 360 m/s

Answer 1

Answer: (D)

360 m/s

Answer 2

We know that the minimum length of the air column in a resonance tube corresponds to the fundamental mode of vibrations. Hence by ignoring end correction. $l=\frac{\lambda}{4}$ $\Rightarrow \lambda=4 l=4 \times 20=80 \,cm =0.8\, m$ Resonant frequency $u=450\, Hz$ $\therefore$ Speed of sound $v=v \lambda$ $=450 \times 0.8=360 \,m / s$