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Waves and Sound — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsWaves and Sound1 Mark
MCQ
A wave of frequency $100 \mathrm{~Hz}$ is sent along a string towards a fixed end. When this wave travels back after reflection, a node is formed at a distance of $10 \mathrm{~cm}$ from the fixed end of the string. The speed of incident (and reflected) wave are
  • A
    $40 \mathrm{~m} / \mathrm{s}$
  • ✓
    $20 \mathrm{~m} / \mathrm{s}$
  • C
    $10 \mathrm{~m} / \mathrm{s}$
  • D
    $5 \mathrm{~m} / \mathrm{s}$
✓

Answer

Correct option: B.
$20 \mathrm{~m} / \mathrm{s}$
At fixed end node is formed and distance between two consecutive nodes $\frac{\lambda}{2}=10 \mathrm{~cm} \Rightarrow \lambda=20 \mathrm{~cm}$
$[\Rightarrow v=n\lambda=20\mathrm{~m} / \mathrm{sec}]$

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