A student sits in the park and measures sound levels by using the standard decibel scale. A nearby radio, playing alone, produces a sound level of 65 dB. Another radio, tuned to a different station, produces 70 dB by itself. What sound level (in dB) would be measured by the student when both radios were on together( not that for independent sound sources, intensities will just add together)
A) 71
B) 72
C) 73
D) 74
E) 75
A) 71
B) 72
C) 73
D) 74
E) 75
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find the intensity of each source:
I(dB)= 10 log[I/10^-12]
for the 65 dB source:
65 = 10 log[I/10^-12]
10^6.5 x 10^-12 = I
I = 3.12x10^-6W/m^2
for the 70 dB source, I = 10^-5
the sum of intensities = 1.32x10^-5 W/m^2
which has a dB value of
I(dB) = 10 log[1.32x10^-5/10^-12] = 71.2
I(dB)= 10 log[I/10^-12]
for the 65 dB source:
65 = 10 log[I/10^-12]
10^6.5 x 10^-12 = I
I = 3.12x10^-6W/m^2
for the 70 dB source, I = 10^-5
the sum of intensities = 1.32x10^-5 W/m^2
which has a dB value of
I(dB) = 10 log[1.32x10^-5/10^-12] = 71.2