Question

A microphone of cross-sectional area 0.80 $c{m}^2$ is placed in front of a small speaker emitting 3.0 W of sound output. If the distance between the microphone and the speaker is 2.0 m, how much energy falls on the microphone in 5.0 s?

• A. $12\mu J$
• B. $80\mu J$
• C. $24\mu J$
• D. $30\mu J$

Answer 1

The correct option is C

$24\mu J$

$\frac{power}{Area}$ for a sphere of radius 2m is $\frac{3}{4\pi (2{)}^2}$

Now to get power being received by microphone

$\frac{3}{16\pi }\times 0.80\times {10}^{-4}$

Energy received in 5 sec

Energy = power $\times$ time

$\frac{3}{16\pi }\times 0.80\times {10}^{-4}\times 5$

$=0.238\times {10}^{-4}$

$=24\times {10}^{-6}J$

$=24\mu J$