Question

Velocity of sound in air is 320 m/s. A pipe closed at one end has a length of 1 m. Neglecting end corrections, the air column in the pipe can resonate for sound of frequency (1) 80 Hz (2) 240 Hz (3) 320 Hz (4) 800 Hz

• A. 1, 2 and 3 are correct
• B. 1 and 2 are correct
• C. 2 and 4 are correct
• D. 1 and 3 are correct

Answer 1

Answer: (B)

For closed pipe $f=n\left(\frac{v}{4l}\right),$
$n=1,3,\mathrm{5......}$
For $n=1$ $f_1=\frac{v}{4l}=\frac{320}{4\times 1}=80Hz$
For $n=3$ $f_3=3f_1=240Hz$
For $n=5$ $f_5=5f_1=400Hz$