Physics (AS & A Level) · Oct / Nov 2019 · Paper 13 · Question 25

A source of sound of constant power P is situated in an open space. The intensity I of sound at distance r from this source is given by I = \frac{P}{4\pi r^2}. How does the amplitude a of the vibrating air molecules vary with the distance r from the source?

1. Aa \propto \frac{1}{r}
2. Ba \propto \frac{1}{r^2}
3. Ca \propto r
4. Da \propto r^2

As printed in the paper