Question

$A$ window whose area is $2m^2$ opens on a street where the street noise result in an intensity level at the window of 60 $dB$. Now, if an acoustic absorber of absorption coefficient 0.6 is fitted at the window, the energy will it collect from street in 5 hours is: ($I_0={10}^{-6}W{m}^{-2}$)

• A. $0.0216J$
• B. $0.216J$
• C. $33610J$
• D. $321.610J$

Answer 1

The correct option is B $0.216J$

We know that:

Sound Level $=10\log \frac{I}{I_0}$

$I=I_0\times {10}^6$ where $I_0={10}^{-12}W{m}^{-2}$

$I={10}^{-6}W{m}^{-2}$

Power falling on the absorber $\left(P_0\right)$ $=Area\times Intensity=2\times {10}^{-6}W$

Power collected by it $\left(P\right)$ $=a\times P=1.2\times {10}^{-6}$

Total energy collected by it $=P\times 5\times 3600=0.216J$