Physics 9702 · AS & A Level · Progressive waves

Progressive waves — practice question

A light beam has power $P$ and a cross-sectional area of $A$. The wave amplitude in the beam is $X$. The beam is then altered so that its frequency stays the same, but its amplitude becomes $4X$ and its cross-sectional area decreases to $\frac{A}{3}$. What is the power of this new beam?

  • A$1.3P$
  • B$5.3P$
  • C$12P$
  • D$48P$

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