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14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
For a certain organ pipe three successive resonance frequencies are observed at $425 \,\,Hz$, $595\,\, Hz$ and $765\,\, Hz$ respectively. If the speed of sound in air is $340 \,\,m/s$, then the length of the pipe is .... $m$
  • A
    $2$
  • B
    $0.4$
  • ✓
    $1$
  • D
    $0.2$
✓

Answer

Correct option: C.
$1$
c
since frequencies are in odd number ratio, the pipe has to be a closed pipe.

Ratio of $3$ frequencies $=425: 595: 765$

$=5: 7: 9$

So fundamental frequency $=f=\frac{425}{5}=85 H z$

For fundamental frequency

$l=\frac{v}{4 f}=\frac{340}{4 \times 85}=1 m$

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