Question

A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $2m$ and $3m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is -

• A. $3:2$
• B. $2:3$
• C. $9:4$
• D. $4:9$

Answer 1

The correct option is C $9:4$

$IntensityofsoundI=\frac{P}{4\pi r^2}$

$or1\propto \frac{1}{r^2}or\frac{I_1}{I_2}=(\frac{r^2}{r^1}{)}^2$

$Here{r}_1=2m,r_2=3m$

$Substitutingthevalues,wehave\frac{I_1}{I_2}=(\frac{3}{2}{)}^2=\frac{9}{4}$

$So,Correctanswerisc$