Physics 9702 · AS & A Level · Progressive waves

Progressive waves — practice question

The sound intensity $I$ varies inversely with the square of the distance $x$ from the sound source. This is expressed as $I \propto \frac{1}{x^2}$. At point P, which is a distance $r$ from the source S, air molecules oscillate with an amplitude of $8.0\,\mu\text{m}$. Point Q is located a distance $2r$ from S. Determine the oscillation amplitude of the air molecules at Q.

  • A$1.4\,\mu\text{m}$
  • B$2.0\,\mu\text{m}$
  • C$2.8\,\mu\text{m}$
  • D$4.0\,\mu\text{m}$

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