Question

The warning tag on a lawn mower states that it produces noise at level of 91.0dB. What is this in Wm^-2?

Answer 1

`1,259mW//m^2`

Explanation:

According to the equation for sound level

`beta = 10 log (I/(I_0))`,

where `beta` is sound level in decibels, `I` is intensity in `W//m^2` and `I_0` is the threshold intensity equal to the minimum that can be heard, which for humans is apparently `10^(-12)W//m^2`.

Substituting in the given data and solving for the required unknown, we get :

`91=10log(I/(10^(-12)))`

#therefore 10^(9,1)=I/(10^-12)

`thereforeI=10^((9,1-12)=)1,259mW//m^2`