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UPSC Civil Service Exam Questions - Engineering

Q1:

Two sources generate noise levels of 90 dB and 94 dB respectively. The cumulative effect of these two noise levels on the human ear is

A 184 dB

B 95.5 dB

C 94 dB

D 92 dB

ANS:B - 95.5 dB

20log{1/N[10^(N1/20)+10^(N2/20)]}
Substituting values N = no. Of sounds.
N1 = sound 1 value,
N2 = sound 2 value,
We get 92.2.
So, option D is the correct answer.