Question

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given
point every minute. Late at night, the traffic flow is only 5 cars per minute. What is the
late-night decibel level?

Answer 1

100 Cars:

db = 10*Log(I/Io)
db = 10*Log(I/10^-12) = 80
Log(I/10^-12) = 8
10^8 = I/10^-12
I = 10^-4 W/m^2.

5 Cars:

I = (5/100) * 10^-4 = 5*10^-6 W/m^2.

db = 10*Log(5*10^-6/10^-12)
db = 10*Log(5*10^6) = 67.

Answer 2

456