Question

The threshold of hearing for the human ear is $10^{-12}\, W \,m ^{-2} .$ This is taken as the standard level. The intensity of sound is $1 \,W \,m ^{-2}$. Expressed in decibel, it has intensity

• A. $10^{12} db$
• B. $12 \,db$
• C. $240\, db$
• D. $120 \,db$

Answer 1

Answer: (D)

Here, Decibel level $=10 \log _{10}\left(\frac{1\, Wm ^{-2}}{10^{-12}\, Wm ^{-2}}\right)$
$=10 \log _{10} 10^{12}=12 \times 10 \,db =120\, db$