The intensity of sound wave while passing through an elastic medium falls down by $10\%$ as it covers one metre distance through the medium. If the initial intensity of the sound wave was $100$ decibels, its value after it has passed through $3$ metre thickness of the medium will be .... $decibel$
Medium
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(b) After passing the $3$ meter intensity is given by 

${I_3} = \frac{{90}}{{100}} \times \frac{{90}}{{100}} \times \frac{{90}}{{100}} \times I = 72.9\% \;{\rm{of }}I$ 

So, the intensity is $72.9$ decibel.

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