Question

A source of sound emits 200`piW` power which is uniformly distributed over a sphere of radius 10 m. What is the loudness of sound on the surface of the sphere?
A. 70 dB
B. 107 dB
C. 80 dB
D. 117 dB

Answer 1

Correct Answer - D
Intensity,
`I=(P)/(A)=(200pi)/(4pixx(10)^2)=0.5(W)/(m^2)`
No. of decibels is given by
`10log_(10)=(I)/(I_0)=10log_(10)((0.5)/(10^-12))`
`=10log_(10)(5xx10^11)`
`10log_(10)((10^12)/(2))`
`=117dB`