# Power and Amplitude of sound wave

1. Nov 6, 2005

### Trooko

For my homework,
To find Amplitude of the wave,
for a longitudinal wave travelling down a copper rod.
Given: frequency, radius of copper rod, average power, Young's constant, density, wavelength.
what equation should I consider?
I'm thinking something like P=(omega*amplitud)^2 because I know power is proportional to amplitude and frequency of the wave....but I know that's wrong.

2. Nov 7, 2005

### Astronuc

Staff Emeritus
The displacement amplitude A is given by:

$$A\,=\,\frac{\Delta{p_o}}{\omega\,\rho\,c}$$, where

$\Delta{p_o}$ is the pressure amplitude,

$\omega$ is the angular frequency given by $2\,\pi\,f$,

$\rho$ is the material density, and

c = speed of sound in the material, which is given by -

$$c = \sqrt{\frac{E}{\rho}}$$

where E is Young's (Elastic) modulus.

The intensity of the sound wave is I = P/a, where P is the power of the wave per unit transverse area, a, and

P = 1/2 $\omega^2$A2$\rho$ c

Last edited: Nov 7, 2005