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A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at distance of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is
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$9: 4$
The average power per unit area that is incident perpendicular to the direction of propagation is called the intensity.
Intensity of sound
$I=\frac{P}{4 \pi r^2}$
or, $I \propto \frac{1}{r^2}$
or, $\frac{I_1}{I_2}=\left(\frac{r_2}{r_1}\right)^2$
here, $r_1=2 \mathrm{~m}, r_2=3 \mathrm{~m}$
Substituting the values, we have
$\frac{I_1}{I_2}=\left(\frac{3}{2}\right)^2=\frac{9}{4}$
Intensity of sound
$I=\frac{P}{4 \pi r^2}$
or, $I \propto \frac{1}{r^2}$
or, $\frac{I_1}{I_2}=\left(\frac{r_2}{r_1}\right)^2$
here, $r_1=2 \mathrm{~m}, r_2=3 \mathrm{~m}$
Substituting the values, we have
$\frac{I_1}{I_2}=\left(\frac{3}{2}\right)^2=\frac{9}{4}$
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