Question

Q.19. The intensity of sound wave gets reduced by 20% while passing through the slab. The reduction in intensity of passage through two such consecutive slabs would be :
(1) 40 %
(2) 36 %
(3) 30 %
(4) 50 %

Answer 1

Dear Student ,

$$\begin{gathered} Let{I}_{0}istheinitialintensity \\ afterpas\sin gfromoneslab,intensityisgivenby: \\ I=I_0-I_0\times \frac{20}{100} \\ I=\frac{4I_0}{5} \\ afterpas\sin gthroughthesecondslab, \\ I\text{'}=I-I\times \frac{20}{100} \\ I\text{'}=I\times \frac{80}{100} \\ I\text{'}=\frac{4I_0}{5}\times \frac{80}{100}=\frac{16}{25}{I}_0 \\ thereforeafterpas\sin gthroughtwosllabsintensityremains64\%oftheinitialvalue. \end{gathered}$$
now reduction in intensity on passage through two consecutive slabs = 100 - 64=36 %
Regards