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)

Let intensity of sound be $l$ and $l^{\prime }$
Loudness of sound initially,
${\beta }_1=10\log \left(\frac{l}{l_0}\right)$
Later ${\beta }_2=10\log \left(\frac{l^{\prime }}{l_0}\right)$
Given, ${\beta }_1-{\beta }_2=20$
$\therefore 20=10\log \left(\frac{l}{l^{\prime }}\right)$
or $l^{\prime }=\frac{l}{100}$
Therefore, intensity decreases by a factor of $100.$