Sound WavesHard
Question
A person speaking normally produces a sound intensity of 40 db at a distance of 1 m. If the threshold intesity for reasonable at which he can be heard clearly is
Options
A.4 m
B.5 m
C.10 m
D.20 m
Solution
Wehave, β = log10 
Where I0 = thershold intensity of sound = 10-12 W/ m2 .....(i)
i.e., 40 = 10 log10
.....(ii)
⇒ 
log10
2 = log10 or 
= 102
∴
= 102(since I ∝ 
)
r22 = 102 r12 or r2 = 10 r1 = 10 × 1 = 10m
Where I0 = thershold intensity of sound = 10-12 W/ m2 .....(i)
i.e., 40 = 10 log10
.....(ii) ⇒ log102 = log10
or = 102∴
= 102(since I ∝ )r22 = 102 r12 or r2 = 10 r1 = 10 × 1 = 10m
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