A source of sound emits $200\pi W$ power which is uniformly distributed over a sphere of $10 m$ radius. What is the loudness of sound on the surface of a sphere
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(c) Intensity = $\frac{{{\rm{power}}}}{{{\rm{area}}}} = \frac{{200\pi }}{{2\pi \times {{10}^{ - 2}}}}$= $1 Watt/m^2$
Now $L = 10{\log _{10}}\frac{I}{{{I_0}}}$= $10{\log _{10}}\left( {\frac{1}{{{{10}^{ - 12}}}}} \right)$
=$10{\log _{10}}{10^{12}} = 120\;dB$
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