Question

A source of sound operates at $2.0kHz,20W$ emitting sound uniformly in all directions. The speed of sound in air is $340m/s$ and the density of air is $1.2$ $kg/m^3$.
What is the intensity at a distance of $6.0m$ from the source?

Answer 1

Here given $V_{air}=340m/s$., Power $=E/t=20W$
$f=2,000Hz,\rho =1.2kg/m^3$
So, intensity $I=E/t.A$
$I=\frac{20}{4\pi r^2}=\frac{20}{4\times \pi \times 6^2}=44mW/m^2$ ( because $r=6m)$