If the warning tag on a lawn mower states that it produces noise at a level of 91.0 dB, what is this in watts per meter squared?

1 Answer
Apr 19, 2015

You can use the relationship:
$I \left(\mathrm{dB}\right) = 10 \log \left(\frac{I}{I} _ 0\right)$
Where ${I}_{0} = {10}^{- 12} \frac{W}{m} ^ 2$ represents the intensity just audible (correspnding to $0 \mathrm{dB}$).
So:
$91 = 10 \log \left(\frac{I}{10} ^ \left(- 12\right)\right)$; power $10$ both sides and rearrange:
$I = 1.25 \times {10}^{-} 3 \frac{W}{m} ^ 2$