## Physics Tutorial

*Point Source Sound*

#### Intro

The intensity of a sound is the amount of energy that passes through a given area in a given time.

I= E/A*t

This equation can also be expressed in terms of power because power is equal to energy over time.

I=P/A

Sound from a point source will radiate from the source in every direction (spherical) such that the intensity of the sound is equal to:

I= P/4πr^2

#### Sample Problem

Sound intensity from a point source will decrease as the square of the distance. You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position?

#### Solution

*It drops to 1/4 its original value

Why?

For a source of a given power P, the intensity is given by I= P/4πr^2. So if the distance doubles, the intensity must decrease to one-quarter its original value.