Question

A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of

• A. 1000
• B. 10000
• C. 10
• D. 100

Answer 1

Answer: (D)

100

Answer 2

Let intensity of sound be $l$ and $l'$
Loudness of sound initially,
$\beta_{1}=10 \log \left(\frac{l}{l_{0}}\right)$
Later $\beta_{2}=10 \log \left(\frac{l'}{l_{0}}\right)$
Given, $\beta_{1}-\beta_{2}=20$
$\therefore 20=10 \log \left(\frac{l}{l^{\prime}}\right)$
or $l'=\frac{l}{100}$
Therefore, intensity decreases by a factor of $100 .$