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 $9m$ and $25m$ respectively from the source. The ratio of the amplitudes of the wave at $P$ and $Q$ is _______.

• A. $25:9$.
• B. $25:19$.
• C. $35:9$.
• D. $125:9$.

Answer 1

The correct option is A $25:9$.

For spherical wave , $I=\frac{I_o}{r^2}$ i.e., $I\propto \frac{1}{r^2}$

$\frac{I_P}{I_Q}=\frac{{\left(25\right)}^2}{{\left(9\right)}^2}\frac{A_P}{A_Q}=\sqrt{{\left(\frac{25}{9}\right)}^2}=25:9$