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

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A string is stretched between two fixed points separated by $75\,cm$ . It is observed to have resonant frequencies of $420\,Hz$ and $315\,Hz$ . There are no other resonant frequencies between these two. Then, the lowest resonant frequency for this string is  ..... $Hz$
  • A
    $10.5$
  • ✓
    $105$
  • C
    $1.05$
  • D
    $1050$
✓

Answer

Correct option: B.
$105$
b
$\frac{\mathrm{n}}{2 l} \mathrm{v}=315 \quad$ and $\quad \frac{(\mathrm{n}+1) \mathrm{v}}{2 l}=420$

Solving $, \frac{\mathrm{v}}{2 l}=105 \mathrm{\,Hz}$

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