Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears ?

Answer

C, D

Explanation

If sound level =120 dB,
then `I=intensity =1W/m^2`
Let the closet distance be x.
`So, Intensity `=(2/(4pix^2))=1`
`rarr x^2(2/(4pi))`
`rarr x=40cm`