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Waves and Sound — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsWaves and Sound1 Mark
MCQ
The phase difference between two points separated by $\mathrm{Im}$ in a wave of frequency $120 \mathrm{~Hz}$ is $90^{\circ}$. The wave velocity is
  • A
    $180 \mathrm{~m} / \mathrm{s}$
  • B
    $240 \mathrm{~m} / \mathrm{s}$
  • ✓
    $480 \mathrm{~m} / \mathrm{s}$
  • D
    $720 \mathrm{~m} / \mathrm{s}$
✓

Answer

Correct option: C.
$480 \mathrm{~m} / \mathrm{s}$
Path difference $\Delta=\frac{\lambda}{2 \pi} \times \phi \Rightarrow 1=\frac{\lambda}{2 \pi} \times \frac{\pi}{2}$
$ \Rightarrow \lambda=4 m$ Hence $v=n \lambda=120 \times 4=480\mathrm{~m} / \mathrm{s}$

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